First, the assessor will want to see your procedure for calculating the uncertainty budgets. The procedure should include a method for identifying all the potential error contributors for a calibration. It should also refer to any software you intend to use and the coverage factor you'll be reporting (usually k=2). You might also want to describe when and why a contributor may be excluded because it won't be significant.
The second area to be reviewed will be the contributors in your uncertainty budgets to see how they were determined. We'll verify the uncertainty from your calibration certificates to make sure they're correct. We'll look at standard error from the calibration certificates, repeatability studies, contributions of environmental variance, deflection, etc.
Last, we'll review uncertainty budgets to make sure you're using the proper distributions in the calculations. It's very important that these are correct because the budgets could be over- or understated dramatically if these are improperly applied.