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t is true that adding a 1Meg paralleled with a 20 pF to the scope input will halve the capacitance, & double the DC resistance. Both of these results will reduce the loading on the DUT, which is the precise reason that 10X probes are used ! The scope's input capacitance is determined by wiring, relays, rotary attenuator switches, etc. All these values are fixed & cannot be made to disappear. There might sometimes be a small trim cap to set capacitance to 20 pF instead of the 18-19 it would otherwise be. This makes all the scopes of the same model look the same so you don't have to keep recompensating probes when they are moved around.