Can CMRR of a data acquisition input be measured this way?
CMRR not just the Common Mode gain, Acm but the rejection ratio of CM gain to DM gain.

Input \$V_{{IN}_{cm}}=\dfrac{V_{in-} + V_{in+}}{2}   \$

\$A_{cm}=\dfrac{V_{{OUT}_{cm}}}{V_{{IN}_{cm}}}   \$   , cm = common mode
\$A_{dm}=\dfrac{V_{{OUT}_{dm}}}{V_{{IN}_{dm}}}   \$    , dm =  diff. mode

\$CMRR=\dfrac{A_{cm}}{A_{dm}}   \$

By nulling input offset to get 0V out, then you can apply Acm input and divide by open loop gain.







simulate this circuit &ndash; Schematic created using CircuitLab

The grounded clock + sine must be within the CM input range.
Then if you have a DAC compare output SINE with input SINE and adjust ratios of Vdm/Vcm until you can see results.   Or you can sweep Vdm instead of a pulse just as long as it is not harmonically related to SINE Vdm .

There may be better ways of analyzing CMRR results with a Spectrum Analyzer or a WAV file on Audacity.exe