(1) ohmmeter reading = dial reading× magnification =150ω×110 =1500ω;

② If the resistance is too large, you should choose to increase the gear, that is, the C gear;

Ohm zero, that is, a;

Re-test, that is, b;

(3) When the battery is not used for a long time, the internal resistance increases, the electromotive force remains basically unchanged, and it can still be zeroed normally;

Because the full bias current Ig is constant, it is given by the following formula:

In the range of Ig=ER, the internal resistance of the ohmmeter is constant in the range of r, and the measured value of the measured resistance is reflected by the pointer of the ammeter. From I=ER +Rx=Ig 1+RxR, it can be known that when r is constant, I is constant, and the pointer is unchanged compared with the original position, so the pointer of the ohmmeter is accurate.

So the answer is:

① 1500Ω;

② Cab;

3 accurate.