I was interested to read that NIST does 40 tape calibrations per year, "mostly for the petroleum and measuring tape manufacturing industry." Does that mean if you are drilling an oil well you need to know how deep you are with a precision of better than 1 in 5000 which is what you would get from a class 2 tape?
The other interesting note was that NIST's temperature controlled tape tunnel can take tapes up to 60m. That must explain why the the tape report shows the tape elasticity was determined for the 40m to 100m interval. This measurement must have been made at the end of the work after the tape had been moved along for the 40m to 100m calibration readings.
The calibration report shows that NIST took readings with 10kg and 20 kg tension, which I did rather wonder about since class 2 tapes are always calibrated at 50N which is close to 5kg about 11 lbs. Perhaps class 1 (ie <0.01% error) tapes are pulled at a higher tension - I cant find the spec at the moment. However, looking at the calibration - this tape was not class 1 at 10kg, but would have been almost spot on at 50N.
Finally, I was interested to compare the picture of the precision laser interferometer which moves on wheels along a precision metal 60m runway, with the following picture of my laser on the back of my bike moving along the calibration course on The Mall: Same measuring principle; different accuracy.
Addition: I have now located the 1973 EU specification for tape measures COUNCIL DIRECTIVE of 19November 1973 on the approximation of the laws of the Member States relating to material measures of length. In the EU, 50N tractive force applies to both class 1 and class 2 tapes.