They are all ways you can make oscilloscope probes that measure current. If you think of a scope as a voltage measurement device, you ought to watch the recent video from Keysight Technology (see ...
[Paul] knew that he could get an oscilloscope that would measure the microamp signals ... He’s trying to visualize what’s going on with the current draw of a microcontroller at various points ...
To determine peak voltage from an oscilloscope trace ... this is not the effective voltage of the trace. A more useful measure of a.c. voltage is the r.m.s. or 'root mean square' voltage.