SATO M84PRO service manual Setting the threshold is

Section 5: Printer Configuration

LCD DISPLAY		DEFINITION
GAP	[X.XXV]	GAP - When setting the “gap” threshold, the voltage shown on the top line of
INPUT	[X.XV]	the display must be measured with nothing but the backing in the sensor and
		then again with a label still attached to the backing. The formula to be used for
		setting the threshold is:
		(High Voltage Level + Low Voltage Level) x 0.5 = Start Value
		1. Insert a label still attached to the backing into the sensor and close the
		Label Hold-Down. Record the voltage shown on the top line of the LCD
		panel. This line should have the message “GAP” on the top line (DIP
		switch DSW2-2 = OFF). Ensure the label is fully under the sensor.
		2. Strip the label from the backing and insert the backing strip under the
		sensor and close the Label Lid. Record the voltage shown on the top line
		of the LCD panel. The voltage ranges measured should be within the
		following ranges:
		Backing with label = 2.0V to 3.5V
		Backing without label = Less than 1.0V
		If the measured values are outside this range, it may be difficult finding a value
		that will work properly under all conditions. If this is the case, a higher quality
		label may be needed to get adequate performance.
		3. Calculate the starting point voltage using the formula.
		4. Use the LINE and FEED keys to step the counter to the desired setting.
		The reading will advance to a setting of 4.9 (the maximum voltage). If a
		value of “0.0” is set, the printer will automatically set the level each time
		the printer is powered on with labels loaded and the head is closed.
		5. Once the setting is correct, pressing the ENTER key will accept the
		setting and advance the next display.

M84Pro Service Manual PN: 9001111A Page 5-18