Equation Required/Formula

If I understand it correctly, it seems like you want to calculate a multiplier value and a floor value (when needed) for non-linear uncertainties. You should be able to use a general approach that works for multiple ranges and non-linear uncertainties. See below for my ideas:

So, assuming you can define a function that represents the relationship between the measured voltage and the uncertainty, we have:

Multiplier = Measured Uncertainty / Uncertainty Function

Use below when the multiplier values are not sufficient to account for the uncertainty, as you mentioned:

Floor Value = Desired Uncertainty - (Multiplier * Measured Voltage)

For each measured voltage, apply the multiplier and add the floor value (if required) to calculate the final uncertainty for the audit. You can apply this method to multiple ranges by repeating the process for each range you want to audit.

You can use a mathematical approach that solves a system of equations. For each range, you can create an equation using the above. For your example, you'll have:

M * 1V + F = 1.7uV
M * 5V + F = 5uV
M * 10V + F = 10uV

Now, you can use a mathematical solver or software to solve this system of equations simultaneously and find values for M and F that satisfy all the above equations.

I hope this answers your question.