I have a Sanwa BX-505 analogue multimeter where the needle wavers and can not be zeroed on the x1, x10 and x1k scales. Zeroing is possible on the x10k scale. The ohmeter is really an electromagnetic voltmeter connected in a circuit with dry cell, resistor, zeroing potentiometer, leads and a subject resistance.

Scans of the relevant pages from the manual are here.
http://carnot.yi.org/SanwaBX505Manual.jpg

What is the cause of this behavior?

Thanks, ... Peter E.