The Spiegel Relaskop is a precision instrument used by foresters and timber cruisers throughout the world. We have tested several to verify the basal area calibration and accuracy.

A brand new relaskop may be slightly out of adjustment, both in terms of focus and calibration. One Forest Service cruiser showed me a brand new relaskop he had used to take a cruising competency test. He failed the test, because the scales in the relaskop were not in focus. This could have been corrected by adjusting the focus ring in the appropriate direction. This is a trial and error process.

Whenever it is out of focus, the relaskop is almost useless, because it cannot be read properly. Once the focus is changed, it may be out of calibration for basal area measurements.

Before testing for calibration, make sure your relaskop is adjusted for level. To test your relaskop for calibration, place a 12” wide target on a wall exactly 16.5 feet from the wall to the center of the relaskop. Use a loggers tape to verify it. While sighting level with the target, the 12” target should exactly fill the 40 factor BAF (i.e. from the left hand measuring edge to the right hand edge of the largest black band). If the relaskop does not read exactly 40 BAF, the relaskop is out of calibration and will definitely give you the WRONG answer when cruising.

Adjusting the focus ring of the relaskop will correct the problem. In most cases, when the relaskop is properly calibrated, the scales are still in focus. If the scales become out of focus as you are calibrating it, refocus the relaskop to make sure you can read the scales properly. Repeat the focusing and calibration process until the instrument is in focus and in calibration.

The red arrow points toward the focus ring