Hi @dandyIdk -
Welcome to the forums!
From what I understand, the calibration Marine Situ performs takes place entirely underwater. It uses the standard checkerboard approach with openCV, as @jackmead515 linked to documentation on here.
This calibration approach makes explicit consideration of things like glass thickness and distances not necessary!
Generally, depth error does increase with distance for stereo cameras in any situation - increasing the baseline separation is the best approach if depth measurements at greater range is required…