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Measure the DC resistance of the Simpson meter movement, with a DMM. Then use the following formula:
The resistance RP to be connected in parallel with an ammeter of full scale current IA and full scale voltage drop VA to increase the full scale current to I is:
RP = VA / (I - IA)
The power P dissipated by the resistance RP with voltage drop VA carrying current (I - IA) is:
P = VA2 / RP = VA(I - IA) = (I - IA)2RP
Note: Use I=250mA, IA=50uA, VA = R(Measured) * 50uA
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