Computers are for geeks, throw them out and drive!
NHRA has changed its thoughts on the window net rule for cars slower than 7.49 (4.50). The section in RED has been REMOVED and replaced by the section in BLUE.
SECTION 20: GENERAL REGULATIONS, INTERIOR: 6, WINDOW NET (Page 29) (3/5/2012) An SFI 27.1 ribbon-type or mesh-type window net is mandatory on any full-bodied car required by the rules to have a roll cage.An SFI 27.1 ribbon-type or mesh-type window net is mandatory on any full-bodied car running 7.49 (*4.49) or quicker. For full-bodied cars running 7.50 (*4.50) to 9.99 (*6.39) or if vehicle runs 135 mph or faster a ribbon-type or SFI 27.1 mesh-type window net is mandatory unless otherwise specified by class requirements. SFI 27.1 window net, when required, must be updated at two-year intervals from the date of manufacture. Window net must be securely mounted on the inside of the roll cage, with the permanent attachment at the bottom. All attachment points must be designed in an attempt to protect the driver and avoid contact with track surface or guardwall. Eyelet clips, dogleash hardware, hose clamps, etc. prohibited. Penetration of webbing, except as performed by manufacturer, prohibited. Any modification to net must be performed by manufacturer.
So you only need an SFI window net if your runing 7.49 or faster. But if your running the "mesh" style you do have to have an SFI replaced every 2 years. The typical Ribon style don't need to be SFI certified nor replace every 2 years.