I purchased a used Weston DC Model 301 meter which is calibrated to
measure from 0 to 10 direct current amperes. I ran some checks on the
meter by using a regulated supply voltage of about 4 volts and some 1 and
10 ohm 10 watt wire wound resistors with the following results:
Measured Voltage Measured Resistance Calculated Current Meter I
Reading
4.10 2.30
1.78 0.8
4.10 1.20
3.42 1.7
3.91 0.70
5.6 3.0
4.10 1.00
4.10 1.8
Comparing the calculated and actual meter readings indicates the meter is
reading about one half actual direct current value. Can you recommend a
repair procedure?

Something doesn't add up: as you go from 1 ohm to 0.7 ohms, the ratio of meter reading to calculated current changes in the wrong direction. Are you sure of your measurements? The numbers you gave aren't consistent enough to be relied on for calibrating the meter.

Presumably the 301 has an internal shunt. There's not much to go wrong, that would cause such a large error. Can you verify the current with a second meter?