The technique I explained has to be done on a scope. I erased the picture that had the x and y axis so I can't say the time scale, but I can put it in perspective. Typically the armatures have 8-12 segments and the pumps spin about 6000rpms. So that makes 48000 to 72000 humps per minute. Divide 60 seconds by that number and you get the time length of one segment.

BTW, the y axis has some identification and it shows 40 and 80mv. The tool used usually is calibarted at 10mv amp or 100mv per amp. Since I know the range of fuel pump current draw to be around 6-8 amps it is plain that the current drops to four amps during the bad segments from around 8amps when performing properly.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician