I have used NI 9235 for strain measurements in the range of 50-300 microstrain.
In my measurement, I always initialize (zero setting) the reading value before starting the test.
I went to website "https://decibel.ni.com/content/docs/DOC-12596 (Accuracy Calculation for the NI 9235)" and use the following formula to calculate the uncertainty.
Uncertainty = Gain Error*reading+Offset Error*Range
When the measured strain is 50 microstrain, the uncertainty is
Uncertainty = (0.02/100)*50 +(0.15/100)*55500 microstrian
= 0.01 + 83
=83 microstrain
My problem is the magnitude of uncertainty due to offset error is large as comparing to the measured value.
I'm not sure about my calculation whether it was correct or not?
Or this device should not be used in this measurement range?
I'm waiting for your suggestion.
Best Regards.
