We offer two different options for timer calibrations: an outside lab, (Transcat) and in-house. There are some differences to know about.
Our outside lab uses the time-base method, of certification, which means they put the timer on a machine called a Timometer to detect the oscillation frequency of the vibrating crystal. This method is very quick, however it only checks the crystal and not the rest of the circuit. (so an overlooked fact is that you really need to do some sort of direct comparison in addition. Our outside lab does not do this double check. (see page 53 7.B.4 of the NIST Practice Guide)
In comparison, we use the Photo Direct Comparison method. (description in section 6.C of the NIST Practice Guide) Essentially we are comparing the result of the timer under test, to a NIST certified timer. In order to eliminate operator timing errors in starting and stopping the device, we use a video to compare the times. This method produces an uncertainty of 5/100 of a second which over the 20 minute duration of the test is 0.005%. We provide the results of the actual time readings found on the certificate with the timer. Here is an example certificate.
