The Selador Switched Linear card, 7400B5615, sends a sense current to the fixture's LEDs. This signal is then converted to voltage and amplified then sent back to the fixture's processor. The processor measures the current to see if it is in the acceptable range predetermined for each color string. If not, it steps up the sense current and sends again until it is within the acceptable range.
To make the fixture auto calibrate:
Press and hold UP and DOWN at the same time until the display says "Cal".
It will then fade on each color as it does the calibration procedure mentioned above.
If there is an issue with any of the colors it will stop the auto calibration procedure at that LED color and display "Err" on the display. The remaining LEDs will not be calibrated until auto calibrate is run again after the problem is fixed.