I'm trying to measure 0 to -130dBm absolute power level using N5531S (opt. 550 sensor) measuring reciver system and then calculate uncertainty for it. Agilent application notes has mentioned that

uncertainty can be calculate using the formula +/-(power meter range 2-4 + 0.005dB/10dB step), but some notes has mentioned about cumulative errors too which should take account? I'm little bit

confused now what formulas and uncertainty things i should take account for my uncertainty budget.

uncertainty can be calculate using the formula +/-(power meter range 2-4 + 0.005dB/10dB step), but some notes has mentioned about cumulative errors too which should take account? I'm little bit

confused now what formulas and uncertainty things i should take account for my uncertainty budget.

Page 12 of the application note has an example for calculating the uncertainty. In that example the input signal is stepped down from 0 dBm to -110 dBm. The application note says what the cumulative errors are. They are +/-(0.015 dB + .005 dB/10 dB step) + Range uncertainty for Range 2 and for Range 3. Also, when below the residual noise floor, you need to account for the contribution from the noise floor by squaring the amount you are below the residual noise floor and multiplying by 0.0012 dB.

Regards -