Velleman CS100 Owner's Manual page 11

Tuning the Detector
TUNE fine-tunes the balance between the detector's receiver and transmitter
circuitry to provide consistent pointer and tone indications.
Follow these steps to set TUNE.
1. Rotate VOLUME to the 11 o'clock position.
2. Set DISCRIMINATION to its midpoint.
3. Hold the search coil about 1 foot (30cm) away from the ground and any
metal object, hold down the red button on the handle, and slowly rotate
TUNE left and right until the pointer on the vu-meter rests at or near 0, then
release the red button.
Red Button
As you search, you can fine-tune the detector using DISCRIMINATION (see
"Fine-Tuning the Detector")
Note :
Press the red button on the handle at any time during operation to
automatically return the pointer to 0.
CS100 10 GB