Howto: Calibrating Y-axis Perpendicular to X-axis

I am about to do a major upgrade on my MMXL and will use it in its current form to machine parts for the upgrade. I wanted to make sure it was calibrated as well as possible.

My X-travel and Y-travel had been adequately calibrated, but upon checking for square, I discovered that X and Y axes were not perfectly perpendicular. The following video shows how I calibrated for squareness.

Note: Before calibrating for perpendicular, you will need to have your travels calibrated already (there are many fine videos on this already). And be warned - you will need to use some basic trigonometry....

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