I think he means;
1) Connect meter lead A to ground (where other end of battery cable attaches to frame, for instance...)
2) Touch meter lead B to negative battery post (sneak it under battery terminal).
3) Remove battery terminal completely from battery.
4) Take reading
The idea here is that the path to ground was never broken. Current used to flow through the ground cable, now it flows through the meter.
Hope that helps...
1986 300E 5-Speed 240k mi.