Tektronix 1A5 Instruction Manual page 13

Source Impedance
100 Ω
stray and lead
10.0000 V
capacitance
Generators
50 Ω
Source Impedance
Fig. 2-3. The effect of difference in source impedance upon apparent CMRR. (Low impedance sources.)
Operating Instructions — Type 1A5
A
9.9990 V
9.9995 V
B
B - A = .0005 V
Apparent DC CMRR
(See graph for effect on AC CMRR)
FREQUENCY
1 MΩ
1 MΩ
= 20,000:1
2-5