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Frank, If you read my above comment I am sure you would agree, even a 1 Meg probe would not affect the readings when marginally saturated with 2 uA pulsed input with 50 nA or even 500 nA from 500 mV= Vbe even though it is only 485 mV with Ic = 12 uA.

Naturally if the input is 0 to 2 uA a FET buffered DIY or TEK probe is desirable but unlikely useful for a non-event since the function of the circuit can be tested with a pulsed >=2 uA input.

I agree with your comment on usefulness , as the 22 Meg is essential to make it work as a sunrise or rise in light current detector to divert the 22 Meg base current.