In the ‘Ratio To Value’ mode, the multimeter dynamically takes measurements from the REAR input terminals, determines a scaling factor for the error and then applies a correction to the measurement on the FRONT input terminals.
For example, a Zener reference with a certified value of 10.000,000V is connected to the REAR input terminals. The RATIO VALUE setting would be set to the certified value and the ratio mode set to RATIO VALUE.
The multimeter was calibrated 180 days ago and has drifted by 2ppm, so the measurement of the 10V on the rear panel is 9.999,980 V. To correct for this the scale factor would be 1.000002. The multimeter dynamically applies this scaling factor to the front panel terminals to correct for the drift of the multimeter as well as any temperature effects.
This mode is best used when performing a transfer between two standards or from a standard to a precision source such as a multi-product calibrator as the multimeter is dynamically compensating for internal errors and the linearity performance of the multimeter can be used to perform an accurate transfer.
To configure the Ratio Value, follow the instructions in this support article : http://support.transmille.com/solution/articles/9000147083.