How do you measure a 45 degree miter to the inside edge?

Finish Carpentry
Trim & Molding

On a mitered piece the inside and outside edges are different lengths, so a single number is ambiguous until you say which edge you meant. Setting the M1 Caliber to 45 degrees and choosing the edge makes the zero account for both kerf and angle, and sliding to length gives the inside dimension directly, 7 and 3/8 here. No deducting the miter by hand.

Which edge the number refers to

Inside and outside edges differ on a miter
Set the M1 to 45 and choose the edge
Zero accounts for kerf and angle
Inside dimension read directly
No deducting the miter by hand

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Tell the tool the angle, then tell it which edge you want. Set the M1 Caliber to 45 degrees and choose inside or outside edge, and zeroing on the blade accounts for both the kerf and the angle. Sliding to length then gives you the inside edge dimension directly, at 7 and 3/8 inches here.