Tried and True.

To you it probably means “tested and found to be reliable/trustworthy.” An example, a few days ago the topic of a car without hydraulic brakes made the rounds. Hydraulic brakes on passenger cars are “tried and true,” we trust them, and are skeptical of a vehicle without them. But that’s not where the phrase originally came from; it’s a centuries old woodworking term.

This is a try square. An OLD tool; examples survive from ancient Egypt. It’s such a basic tool that it’s often used as the symbol of the carpentry trade. “Try” in this case means “examine” rather than “attempt”, more like how a judge “tries” a case than a jedi trainee “tries” to lift an X-wing out of a swamp. A try square is used to examine a board. For squareness, and possibly also straightness and flatness. A board that passes this exam is said to be “true.”

“True” meaning straight, flat, parallel or even concentric is still in use to this day; “truing” a surface means to flatten it.