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Knowing that the Vbe is less than 500 mV with a 10 Meg probe will draw less than 50 nA meanwhile the base current for Vbe= 500 mV is several uA. Do you really think 50nA shunt on the base will make any errors?  This is because the incremental impedance is a lot lower than the linear equivalent = Vbe/Ib.

Below the variable 0 to 10 uA current source is series modulated with the left NPN and clock. while a 10 Meg probe is added to Vbe with current shown.

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