Mine has allways ran identical times from track 1/8th mile converted to 60 mph and gtech 60 mph. Allways identical. I reckon if you put a track 1/8th mile time in there (which will be alot lower in mph than the 1/8th mile the modern gtech gives of course) you will see that's what it runs within a couple percent, it's very accurate. Mack I dunno what drugs you used to get 4.2
you need to use a 1/8th mile time slip. The other calculators are for drag cars with ideal gearing etc and pointless for a street car.
Immortality, you will be able to use that calculator to reverse engineer your 1/8th mile ET and gtech 60 mph ET to find out what your track 1/8th mile mph would be (I'd guess about 3mph less than it shows on the gtech)