An LF356 op amp is used as a gain amplifier with the output taken across R5, When a full-scale current of 1 mA is flowing
through the meter, exactly 1 V appears across R5 (should be 1% tolerance or better). This is fed back to R2 to the summing junction of IC1 (a full-scale produces ). This offsets the current through Rl. Rl has a value of 1 /V which is used to zero the meter. R4 provides some overcur-rent protection for the meter.