Type B Uncertainty and TUR

For a calibration test method of a tachometer in the estimation of uncertainty I used the Type B uncertainty as per the NIST Technical Note. Because this is something fairly new Id like the opinion of other people who work in the field about how I stated to calculated the Uncertainties and the TUR.
The tachometer to be calibrated has a digital display and divisions of 1rpm, so for the UUC the uncertainty is calculated using the 1rpm and 1rpm rpm as lower and upper limits for a- and a+ respectively. The probability of occurrence of the values is modeled as a rectangular distribution.

So U=a/(3)^(1/2), U=0.6rpm

The uncertainty of the Standard in the calibration certificate is very low(~0.007rpm), but to overcome some variances in the reading the lower and upper limits of a are 0.1rpm, then doing the same as for the UUC the uncertainty for the Standard is S=0.06rpm.

And the TUR is r:1, for U=r*S. So the TUR is 10:1.

Please post comments, and suggestions.