Hi Jeff,
I agree that there is a bit of an error and that would be important IF we needed to know the exact VTF at a very specific height. If this were the case cartridge makers would never have trusted us all of these years with that little Shure balance beam. However, it is consistency that is most important. It is ok be off from that ideal measurement by just a bit as long as every measurement you make has that same small error. This only becomes an issue if you start comparing notes with someone else about their VTF settings with the same cartridge. My opinion is that if you keep in mind that there could be a few hundredths of a gram difference and do final adjustments based on the sound it is hard to go wrong. But, if you want to build one of those out-rigger jigs to get closer to the exact record surface it certainly couldn't hurt to know what the difference in measurements is.
Yes, you did well on the price. I saw AcousTech and assumed you bought it from one of those vendors charging twice the price. That's what I get for assuming!
Best,
Dan