You clear the Speed Through Water (STW) calibration on individual DSM200s or DSM250s in the following way. Enter the menu mode, scroll to "Configuration..." and press enter. Scroll to "Device Configuration..." and press enter. Scroll to the DST100 and press enter. Scroll to "Clear Speed Calibration" and press enter. Scroll to "Clear" and press enter. Notice that the number changes to 1.000 which indicates that the display now multiplies all DST100 STW values by 1. This effectively zeros out the DST100 STW calibration. Since the calibration data is not stored in the DST100 but rather in the individual displays, each DSM200 or DSM250 must be cleared in the same way.