Prosecution Insights
Last updated: July 17, 2026
Application No. 19/173,092

SEAM CONSTRUCTION USING RADIO FREQUENCY WELDING AND TAPE

Non-Final OA §103§DP
Filed
Apr 08, 2025
Priority
Jul 14, 2020 — continuation of 16/927,989 +3 more
Examiner
CAILLOUET, CHRISTOPHER C
Art Unit
1746
Tech Center
1700 — Chemical & Materials Engineering
Assignee
Weltop Outdoor (Hk) Co. Ltd.
OA Round
1 (Non-Final)
68%
Grant Probability
Favorable
1-2
OA Rounds
1y 8m
Est. Remaining
83%
With Interview

Examiner Intelligence

Grants 68% — above average
68%
Career Allowance Rate
514 granted / 759 resolved
+2.7% vs TC avg
Strong +15% interview lift
Without
With
+15.2%
Interview Lift
resolved cases with interview
Typical timeline
2y 12m
Avg Prosecution
17 currently pending
Career history
779
Total Applications
across all art units

Statute-Specific Performance

§101
0.9%
-39.1% vs TC avg
§103
76.2%
+36.2% vs TC avg
§102
3.5%
-36.5% vs TC avg
§112
10.1%
-29.9% vs TC avg
Black line = Tech Center average estimate • Based on career data from 759 resolved cases

Office Action

§103 §DP
DETAILED ACTION Notice of Pre-AIA or AIA Status The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA . In the event the determination of the status of the application as subject to AIA 35 U.S.C. 102 and 103 (or as subject to pre-AIA 35 U.S.C. 102 and 103) is incorrect, any correction of the statutory basis for the rejection will not be considered a new ground of rejection if the prior art relied upon, and the rationale supporting the rejection, would be the same under either status. Claim Interpretation Claims 12-20 are drawn to a “manufacturing system”. Examiner notes that the definition of “system” being used is “a formulated plan and/or procedure” (i.e. a method) instead of meaning “a recited apparatus structure and possibly the materials worked upon” as is common with system type claims. Claim Rejections - 35 USC § 103 The following is a quotation of 35 U.S.C. 103 which forms the basis for all obviousness rejections set forth in this Office action: A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains. Patentability shall not be negated by the manner in which the invention was made. Claims 1-20 is/are rejected under 35 U.S.C. 103 as being unpatentable over Wangbunyen et al. (US 8741412) in view of Seiders et al. (US 9139352). As to claim 1, Wangbunyen discloses a process of constructing an air tight and water tight seam (formation of effective waterproof and hydrostatically sealed seam, where the hydrostatic seal may or may not allow passage of gas molecules; column 4, lines 26-38; column 5, lines 6-15; column 7, lines 45-50), comprising: cutting two panels of a sheet of material made of a selected first material (fabric stacks (sheet of material) comprising a first and second piece of laminated fabric 105,110 (two panels), subjected to cutting operation in cutting anvil 130 along aligned edge; figure 1; column 6, lines 5-15); sealing the two panels at a respective selected edge of each of the two panels using an ultrasonic machine (first and second piece of laminated fabric 105,110 (two panels) sealed ultrasonically using ultrasonic welding machine 125 along aligned edge; figure 1; column 6, lines 5-35), forming a seam (first and second piece of laminated fabric are sealed ultrasonically to form a seam; abstract; figure 1; column 6, lines 5-35); overlaying the seam with a section of tape (seam tape 300 is applied along a portion of the seam, where seam tape is formed of adhesive hydrostatic polymer; figure 3; column 6, lines 45-60; column 8, lines 5-26); and sealing the section of tape and the seam using a radio frequency (RF) welding machine (tape seam applied over ultrasonic seam, where welding operation can be carried out using welding tool (RF welding machine) generating radio frequency radiation; figure 1; column 6, lines 5-65; column 7, lines 1-10, 20-30; column 8, lines 24-30; column 10, lines 6-10). Wangbunyen does not explicitly disclose constructing an air tight seam; cutting a sheet of material made of a selected first material into two panels; and the section of tape made of the selected first material. Seiders discloses constructing an air tight seam (assembly can be pressurized up to 14 psi above atmospheric pressure with compressed air; column 5, lines 25-35); cutting a sheet of material made of a selected first material into two panels (outer shell portions 501a, 501b (panels), and also portions (panels) of insulating layer 502, of an insulating device can be cut to size from stock material; figures 5A, 6; column 4, lines 24-29; column 6, lines 13-16); and a section of tape comprising a selected first material (top inner liner 500a, middle 500b and bottom portion 500c are secured together using TPU tape, where liner material is also TPU nylon; column 3, lines 15-25; column 8, lines 5-15). It would have been obvious to one of ordinary skill in the art at the time of the invention to modify the Wangbunyen invention to provide cutting a sheet of material made of a selected first material into two panels; and overlaying the seam with a section of tape made of the selected first material, as taught by Seiders, in order to allow ordering of bulk stock material and integrate cutting pieces for assembly into the process, which provides for more control and economies of scale, and further to provide a compatible tape placed over the seams to maintain air tight and waterproof qualities of chamber liner (Seiders; column 3, lines 15-30). As to claim 2, the method of claim 1 is taught as seen above. Wangbunyen further discloses wherein the section of tape is further coated with a second material on one side of the section of tape before the overlaying step (adhesive tape 300 comprises multiple layers 410, 405, 400, where hydrostatic polymer layer 405 and adhesive layer 410 (second material) are adjacent to outer shell fabric layer 400 (coated before overlaying step); figures 3-4; column 7, lines 50-67; column 8, lines 1-4). As to claim 3, the method of claim 2 is taught as seen above. Wangbunyen further discloses wherein the second material is polyurethane (PU) (adhesive hydrostatic polymer comprises polyurethane in a short list, and layer 405 is constructed of the same material as the hydrostatic polymer; figure 4; column 4, lines 10-20; column 7, lines 65-67; column 8, lines 1-2; claim 5). As to claim 4, the method of claim 2 is taught as seen above. Wangbunyen does not disclose wherein the second material is thermoplastic polyurethane (TPU). An embodiment of Seiders discloses wherein the second material is thermoplastic polyurethane (TPU) (top inner liner 500a, middle 500b and bottom portion 500c are secured together using TPU tape, where liner material is also TPU nylon; column 3, lines 15-25; column 8, lines 5-15). It would have been obvious to one of ordinary skill in the art at the time of the invention to modify the Wangbunyen invention to provide overlaying the seam with a section of tape made of the selected first material, as taught by Seiders, in order to provide a compatible tape placed over the seams to maintain waterproof qualities of chamber liner (Seiders; column 3, lines 15-30). As to claim 5, the method of claim 2 is taught as seen above. Wangbunyen further discloses wherein the second material is one of Polyvinyl Chloride (PVC), Ethylene-Vinyl Acetate (EVA), Polytetrafluoroethylene (PTFE) (adhesive hydrostatic polymer comprises PTFE in a short list, and layer 405 is constructed of the same material as the hydrostatic polymer; figure 4; column 4, lines 10-20; column 7, lines 65-67; column 8, lines 1-2; claim 5), or a combination thereof. As to claim 6, the method of claim 2 is taught as seen above. Wangbunyen further discloses wherein the overlaying step comprises overlaying the coated side of the section of tape against the seam (as shown in figures 3-4, hydrostatic polymer layer 405 and adhesive layer 410 (second material) are placed facing seam and outer shell fabric layer 400 faces away from the seam; figures 3-4; column 7, lines 50-67; column 8, lines 1-4). As to claim 7, the method of claim 1 is taught as seen above. Wangbunyen further discloses wherein an area adjacent to both sides of the seam and along a length of the seam is further coated a third material before the overlaying step (adhesive strips 115and120 coat a portion of left and right sides of outer face 205, respectively, along the length of the seam, prior to application of seam tape; figure 2; column 7, lines 28-55). As to claim 8, the method of claim 7 is taught as seen above. Wangbunyen further discloses wherein the third material is polyurethane (PU) (suitable adhesive polymers include polyurethanes, in a short list; column 5, lines 15-16). As to claim 9, the method of claim 7 is taught as seen above. Wangbunyen does not disclose wherein the third material is thermoplastic polyurethane (TPU). An embodiment of Seiders discloses wherein the third material is thermoplastic polyurethane (TPU )(top inner liner 500a, middle 500b and bottom portion 500c are secured together using TPU tape, where liner material is also TPU nylon; column 3, lines 15-25; column 8, lines 5-15). It would have been obvious to one of ordinary skill in the art at the time of the invention to modify the Wangbunyen invention to provide overlaying the seam with a section of tape made of the selected first material, as taught by Seiders, in order to provide a compatible tape placed over the seams to maintain waterproof qualities of chamber liner (Seiders; column 3, lines 15-30). As to claim 10, the method of claim 7 is taught as seen above. . Wangbunyen does not disclose wherein the third material is one of Polyvinyl Chloride (PVC), Ethylene-Vinyl Acetate (EVA), Polytetrafluoroethylene (PTFE), or a combination thereof. An embodiment of Seiders discloses a laminate structure comprising Polyvinyl Chloride (PVC) (PVC; column 8, lines 9-19), Ethylene-Vinyl Acetate (EVA) (EVA; column 8, lines 39-40). In order to match or coordinate with other layers (Wangbunyen; column 7, lines 56-64), it would have been obvious to one of ordinary skill in the art at the time of the invention to modify the Wangbunyen invention to provide wherein the third material is one of Polyvinyl Chloride (PVC), Ethylene-Vinyl Acetate (EVA), as taught by Seiders within reasonable experimentation, in order to provide a compatible tape placed over the seams to maintain waterproof qualities of chamber liner (Seiders; column 3, lines 15-30). As to claim 11, the method of claim 1 is taught as seen above. Wangbunyen further discloses wherein the panels are cut based on one or more specifications of a desired product. Seiders discloses wherein the panels are cut based on one or more specifications of a desired product (outer shell portions 501a, 501b (panels), and also portions (panels) of insulating layer 502, of an insulating device can be cut to size from stock material, where cutting tool 700 cuts base portion of insulating layer to size from stock foam in order to form insulating device that forms a chamber/receptacle 504; figures 1, 5A, 6; column 2, lines 35-45; column 4, lines 24-29; column 6, lines 13-30). It would have been obvious to one of ordinary skill in the art at the time of the invention to modify the Wangbunyen invention to provide wherein the panels are cut based on one or more specifications of a desired product, as taught by Seiders, in order to provide an insulating waterproof receptacle (Seiders; column 2, lines 45-60). As to claim 12, Wangbunyen discloses a manufacturing system for constructing an air tight and water tight seam (formation of effective waterproof and hydrostatically sealed seam, where the hydrostatic seal may or may not allow passage of gas molecules; column 4, lines 26-38; column 5, lines 6-15; column 7, lines 45-50), the manufacturing system constructing the air tight and water tight seam comprising the steps of: cutting two panels of a sheet of material made of a selected first material (fabric stacks (sheet of material) comprising a first and second piece of laminated fabric 105, 110 (two panels), subjected to cutting operation in cutting anvil 130 along aligned edge; figure 1; column 6, lines 5-15); sealing the two panels at a respective selected edge of each of the two panels using an ultrasonic machine (first and second piece of laminated fabric 105, 110 (two panels) sealed ultrasonically using ultrasonic welding machine 125 along aligned edge; figure 1; column 6, lines 5-35), forming a seam (first and second piece of laminated fabric are sealed ultrasonically to form a seam; abstract; figure 1; column 6, lines 5-35); overlaying the seam with a section of tape (seam tape 300 is applied along a portion of the seam, where seam tape is formed of adhesive hydrostatic polymer; figure 3; column 6, lines 45-60; column 8, lines 5-26); and sealing the section of tape and the seam using a radio frequency (RF) welding machine (tape seam applied over ultrasonic seam, where welding operation can be carried out using welding tool (RF welding machine) generating radio frequency radiation; figure 1; column 6, lines 5-65; column 7, lines 1-10, 20-30; column 8, lines 24-30; column 10, lines 6-10). Wangbunyen does not explicitly disclose constructing an air tight seam; cutting a sheet of material made of a selected first material into two panels; and the section of tape made of the selected first material. Seiders discloses constructing an air tight seam (assembly comprising seams can be pressurized up to 14 psi above atmospheric pressure with compressed air; column 5, lines 25-35); cutting a sheet of material made of a selected first material into two panels (outer shell portions 501a, 501b (panels), and also portions (panels) of insulating layer 502, of an insulating device can be cut to size from stock material; figures 5A, 6; column 4, lines 24-29; column 6, lines 13-16); and a section of tape comprising a selected first material (top inner liner 500a, middle 500b and bottom portion 500c are secured together using TPU tape, where liner material is also TPU nylon; column 3, lines 15-25; column 8, lines 5-15). It would have been obvious to one of ordinary skill in the art at the time of the invention to modify the Wangbunyen invention to provide cutting a sheet of material made of a selected first material into two panels; and overlaying the seam with a section of tape made of the selected first material, as taught by Seiders, in order to allow ordering of bulk stock material and integrate cutting pieces for assembly into the process, which provides for more control and economies of scale, and further to provide a compatible tape placed over the seams to maintain air tight and waterproof qualities of chamber liner (Seiders; column 3, lines 15-30). As to claim 13, the system of claim 12 is taught as seen above. Wangbunyen further discloses wherein the section of tape is further coated with a second material on one side of the section of tape before the overlaying step (adhesive tape 300 comprises multiple layers 410,405,400, where hydrostatic polymer layer 405 and adhesive layer 410 (second material) are adjacent to outer shell fabric layer 400 (coated before overlaying step); figures 3-4; column 7, lines 50-67; column 8, lines 1-4). As to claim 14, the system of claim 13 is taught as seen above. Wangbunyen further discloses wherein the second material is polyurethane (PU) (adhesive hydrostatic polymer comprises polyurethane in a short list, and layer 405 is constructed of the same material as the hydrostatic polymer; figure 4; column 4, lines 10-20; column 7, lines 65-67; column 8, lines 1-2; claim 5). As to claim 15, the system of claim 13 is taught as seen above. Wangbunyen further discloses wherein the second material is one of polyurethane (PU), thermoplastic polyurethane (TPU), Polyvinyl Chloride (PVC), Ethylene Vinyl Acetate (EVA), Polytetrafluoroethylene (PTFE) (adhesive hydrostatic polymer comprises PTFE in a short list, and layer 405 is constructed of the same material as the hydrostatic polymer; figure 4; column 4, lines 10-20; column 7, lines 65-67; column 8, lines 1-2; claim 5), or a combination thereof. As to claim 16, the system of claim 13 is taught as seen above. Wangbunyen further discloses wherein the overlaying step comprises overlaying the coated side of the section of tape against the seam (as shown in figures 3-4, hydrostatic polymer layer 405 and adhesive layer 410 (second material) are placed facing seam and outer shell fabric layer 400 faces away from the seam; figures 3-4; column 7, lines 50-67; column 8, lines 1-4). As to claim 17, the system of claim 12 is taught as seen above. Wangbunyen further discloses wherein an area adjacent to both sides of the seam and along a length of the seam is further coated a third material before the overlaying step (adhesive strips 115 and 120 coat a portion of left and right sides of outer face 205, respectively, along the length of the seam, prior to application of seam tape; figure 2; column 7, lines 28-55). As to claim 18, the system of claim 17 is taught as seen above. Wangbunyen further discloses wherein the third material is polyurethane (PU) (suitable adhesive polymers include polyurethanes, in a short list; column 5, lines 15-16). As to claim 19, the system of claim 17 is taught as seen above. Wangbunyen does not disclose wherein the third material is one of Polyvinyl Chloride (PVC), Ethylene-Vinyl Acetate (EVA), Polytetrafluoroethylene (PTFE), or a combination thereof. An embodiment of Seiders discloses a laminate structure comprising Polyvinyl Chloride (PVC) (PVC; column 8, lines 9-19), Ethylene-Vinyl Acetate (EVA) (EVA; column 8, lines 39-40). In order to match or coordinate with other layers (Wangbunyen; column 7, lines 56-64), it would have been obvious to one of ordinary skill in the art at the time of the invention to modify the Wangbunyen invention to provide wherein the third material is one of Polyvinyl Chloride (PVC), Ethylene-Vinyl Acetate (EVA), as taught by Seiders within reasonable experimentation, in order to provide a compatible tape placed over the seams to maintain waterproof qualities of chamber liner (Seiders; column 3, lines 15-30). As to claim 20, the system of claim 12 is taught as seen above. Wangbunyen does not disclose wherein the panels are cut based on one or more specifications of a desired product. Seiders discloses wherein the panels are cut based on one or more specifications of a desired product (outer shell portions 501a, 501b (panels), and also portions (panels) of insulating layer 502, of an insulating device can be cut to size from stock material, where cutting tool 700 cuts base portion of insulating layer to size from stock foam in order to form insulating device that forms a chamber/receptacle 504; figures 1, 5A, 6; column 2, lines 35-45; column 4, lines 24-29; column 6, lines 13-30). It would have been obvious to one of ordinary skill in the art at the time of the invention to modify the Wangbunyen invention to provide wherein the panels are cut based on one or more specifications of a desired product, as taught by Seiders, in order to provide an insulating waterproof receptacle (Seiders; column 2, lines 45-60). Double Patenting The nonstatutory double patenting rejection is based on a judicially created doctrine grounded in public policy (a policy reflected in the statute) so as to prevent the unjustified or improper timewise extension of the “right to exclude” granted by a patent and to prevent possible harassment by multiple assignees. A nonstatutory double patenting rejection is appropriate where the conflicting claims are not identical, but at least one examined application claim is not patentably distinct from the reference claim(s) because the examined application claim is either anticipated by, or would have been obvious over, the reference claim(s). See, e.g., In re Berg, 140 F.3d 1428, 46 USPQ2d 1226 (Fed. Cir. 1998); In re Goodman, 11 F.3d 1046, 29 USPQ2d 2010 (Fed. Cir. 1993); In re Longi, 759 F.2d 887, 225 USPQ 645 (Fed. Cir. 1985); In re Van Ornum, 686 F.2d 937, 214 USPQ 761 (CCPA 1982); In re Vogel, 422 F.2d 438, 164 USPQ 619 (CCPA 1970); In re Thorington, 418 F.2d 528, 163 USPQ 644 (CCPA 1969). A timely filed terminal disclaimer in compliance with 37 CFR 1.321(c) or 1.321(d) may be used to overcome an actual or provisional rejection based on nonstatutory double patenting provided the reference application or patent either is shown to be commonly owned with the examined application, or claims an invention made as a result of activities undertaken within the scope of a joint research agreement. See MPEP § 717.02 for applications subject to examination under the first inventor to file provisions of the AIA as explained in MPEP § 2159. See MPEP § 2146 et seq. for applications not subject to examination under the first inventor to file provisions of the AIA . A terminal disclaimer must be signed in compliance with 37 CFR 1.321(b). The USPTO Internet website contains terminal disclaimer forms which may be used. Please visit www.uspto.gov/patent/patents-forms. The filing date of the application in which the form is filed determines what form (e.g., PTO/SB/25, PTO/SB/26, PTO/AIA /25, or PTO/AIA /26) should be used. A web-based eTerminal Disclaimer may be filled out completely online using web-screens. An eTerminal Disclaimer that meets all requirements is auto-processed and approved immediately upon submission. For more information about eTerminal Disclaimers, refer to www.uspto.gov/patents/process/file/efs/guidance/eTD-info-I.jsp. Claims 1-20 are rejected on the ground of nonstatutory double patenting as being unpatentable over claims 1-6 of U.S. Patent No. 10,751,948. Although the claims at issue are not identical, they are not patentably distinct from each other because: As to claim 1, Claim 1 of ‘948 recites all of the limitations of claim 1 and it would have been obvious to eliminate any extra recited steps in claim 1 of ‘948 since the deletion of unwanted process steps is an obvious expedient. In re Kuhle, 526 F.2d 553, 188 USPQ 7 (CCPA 1975). As to claims 2-5, the method of claim 1 is taught as seen above. Claims 2-5 are rejected for the same reasons as claim 1 above since claim 1 of ‘948 recites the same materials that are coated upon the tape. As to claim 6, the method of claim 2 is taught as seen above. Claim 2 of ‘948 recites the overlaying step comprises overlaying the coated surface of the tape against the seam. As to claims 7-10, the method of claim 1 is taught as seen above. Claims 7-10 are rejected for the same reasons as claim 1 above since claim 1 of ‘948 recites the same materials that are coated upon side of the seam. As to claim 11, the method of claim 1 is taught as seen above. Claim 3 of ‘948 recites the same limitations as claim 11. Claim 12 is rejected over claim 4 of ‘948 for the same reasons as claim 1 above. As to claims 13-15, the method of claim 12 is taught as seen above. Claims 13-15 are rejected for the same reasons as claim 12 above since claim 4 of ‘948 recites the same materials that are coated upon the tape. As to claim 16, the method of claim 13 is taught as seen above. Claim 5 of ‘948 recites the overlaying step comprises overlaying the coated surface of the tape against the seam. As to claims 17-19, the method of claim 12 is taught as seen above. Claims 17-19 are rejected for the same reasons as claim 12 above since claim 4 of ‘948 recites the same materials that are coated upon the tape. As to claim 20, the method of claim 12 is taught as seen above. Claim 6 of ‘948 recites the same limitations as claim 20. Conclusion Any inquiry concerning this communication or earlier communications from the examiner should be directed to CHRISTOPHER C CAILLOUET whose telephone number is (571)270-3968. The examiner can normally be reached on M-F 9AM-5PM EST. Examiner interviews are available via telephone, in-person, and video conferencing using a USPTO supplied web-based collaboration tool. To schedule an interview, applicant is encouraged to use the USPTO Automated Interview Request (AIR) at http://www.uspto.gov/interviewpractice. If attempts to reach the examiner by telephone are unsuccessful, the examiner’s supervisor, PHILLIP TUCKER can be reached on (571)272-1095. The fax phone number for the organization where this application or proceeding is assigned is 571-273-8300. Information regarding the status of an application may be obtained from the Patent Application Information Retrieval (PAIR) system. Status information for published applications may be obtained from either Private PAIR or Public PAIR. Status information for unpublished applications is available through Private PAIR only. For more information about the PAIR system, see https://ppair-my.uspto.gov/pair/PrivatePair. Should you have questions on access to the Private PAIR system, contact the Electronic Business Center (EBC) at 866-217-9197 (toll-free). If you would like assistance from a USPTO Customer Service Representative or access to the automated information system, call 800-786-9199 (IN USA OR CANADA) or 571-272-1000. /CHRISTOPHER C CAILLOUET/Examiner, Art Unit 1745 /GEORGE R KOCH/Primary Examiner, Art Unit 1745
Read full office action

Prosecution Timeline

Apr 08, 2025
Application Filed
Jul 01, 2026
Non-Final Rejection mailed — §103, §DP (current)

Precedent Cases

Applications granted by this same examiner with similar technology

Patent 12667500
ARTICLES WITH ZONED APERTURED MATERIALS AND REGISTRATION METHODS
3y 1m to grant Granted Jun 30, 2026
Patent 12653725
ABSORBENT ARTICLES AND METHODS OF MAKING THE SAME
3y 5m to grant Granted Jun 16, 2026
Patent 12654407
Automated Fiber Placement System Configured to Lay Down a Plurality of Widths of Composite Tapes
3y 0m to grant Granted Jun 16, 2026
Patent 12642711
METHOD AND APPARATUS FOR BONDING ELASTIC PARTS UNDER TENSION TO AN ADVANCING CARRIER
1y 9m to grant Granted Jun 02, 2026
Patent 12599508
ABSORBENT ARTICLES AND METHODS FOR MAKING ABSORBENT ARTICLES WITH FRANGIBLE PATHWAYS
2y 9m to grant Granted Apr 14, 2026
Study what changed to get past this examiner. Based on 5 most recent grants.

Strategy Recommendation AI-generated — please review before filing

Get a prosecution strategy drawn from examiner precedents, rejection analysis, and claim mapping.
Typically takes 5-10 seconds — AI-generated, attorney review required before filing

Prosecution Projections

1-2
Expected OA Rounds
68%
Grant Probability
83%
With Interview (+15.2%)
2y 12m (~1y 8m remaining)
Median Time to Grant
Low
PTA Risk
Based on 759 resolved cases by this examiner. Grant probability derived from career allowance rate.

Sign in with your work email

Enter your email to receive a magic link. No password needed.

Personal email addresses (Gmail, Yahoo, etc.) are not accepted.

Free tier: 3 strategy analyses per month