The exposure meter knob replaces the standard winding knob on Hasselblad 500-series cameras. It has a built-in selenium cell meter eliminating the need for batteries. The exposure meter converts lights intensity to EV values.This meter offers incident and reflected light metering modes. Results are displayed using a simple meter needle. It can be quickly removed to capture meter readings close to the subject. Recalibration of the meter needle is performed by covering the cell completely blocking all light. Once completed, the meter needle should point to the small white line at the left of the scale.