Using calipers to take measurements
Turn on the calipers (some types will turn on when you open them and also turn off automatically). Make sure the scale is set to millimeters, not inches. Close the jaws of the calipers firmly and make sure the display shows 0.00. If not, press the reset button to read 0.00. (You should perform this check before every measurement.)
To make the measurement, use the jaws on the top side of the calipers, that measure inside distances, as in the photo below (Figure 11). Place the jaws in the top corners of the window. Use the thumb wheel on the calipers to move the jaws. Both jaws should fit snugly, but don't use so much pressure that you distort the window. Record the gap width to two decimal places - do not round up.
Figure 11
In case either edge of the window is uneven, position the corresponding jaw of the calipers where it fits most easily and securely, and make a mark on the band with the black permanent marker to mark that spot for use in future measurements.
After you have installed a dendrometer band and recorded your initial measurement, the band might need some time to settle into place – this can be 1-2 weeks. Typically, the tighter the band, the shorter the time to settle in. After this time, the gap will have stabilized, and you will be able to make reliable readings.
As you take readings, record information about factors that could affect the tree's growth, such as temperature, recent rainfall, time of day, etc. You should also make sure your readings are consistent with ambient conditions and with recent measurements for the same tree. For example, an unusually large increase might be expected if there has been a lot of rain, but if the weather has been very dry you may see shrinkage. If your reading is unaccountably greater or less than preceding ones, recheck your measurement. If you are sure it's correct, make a note that you checked it. When you have completed the measurements, turn off the caliper (if it doesn't do so automatically).