How "square" is your framing square ?

Have you ever wondered if the rusty framing square hanging in your shop is exactly 90* ?
If you are at all like me, I never bothered to check it since the day I bought it. I had to setup a Chop Shot Guide for my skill saw and I needed a true square to reference the Chop Shot Guide.

A very quick test told me my framing square was not 90* , more like 88* (if I had to guess).
With the longest edge of my framing square against a straight piece of wood I made one line with my pencil down the shorter length of the square. Flipped the square 180* and made another line close to the first one. If the lines intersect or are anything but parallel an adjustment is necessary.

I recalled an article in a wood working magazine on the very subject - how to true your framing square.  To correct an acute angle(less than 90*) take a small punch or nail set and use a hammer to strike the  inside corner of the square(make sure the square is backed up by something hard ie: concrete or steel). Run the test for square again to see if further adjustment is necessary.
Alternately if your square is an obtuse angle(greater than 90*) strike the square on the outside corner to bring the angle down closer to 90*. You might notice that the inside corner of the square is relieved by a small  arc. This is to allow the steel to move when adjustments are made.

When you can draw two parallel lines with your square(using the test above) you can be sure it is exactly 90*.  How will you know if the lines are parallel? Your brain knows parallel lines when it sees them so trust your judgement on this.

Congratulations you now own a calibrated framing square! So the next time the square falls down on the floor you can to a quick check/adjustment and get back to the fun stuff.