VSMA screen calc method100. Factor 'G" –. Screen Sutace. Open Area. Applies when open area of screening sumace is less than open area shown in Factor "A" capacity chart Factor. "G" = The VSMA torm Vibrating Screen Questionnaire" should be used as a guide to record the application data necessary to apply the above formula. When using the.vibrating screen g value by vsma,Vibrating Screen Sizing Formula by VSMA - bulk-online ForumsJan 31, 2004 . Here is some very critical information to size vibrating screens to do the TONS PER HOUR and opening size you desire. Any Questions please ask here. regards, George Baker, vibrating screen consultant & Moderator.