I looked at new framing squares on-line. Reviews were mixed. Some found the square they purchased to be square. Others found the same makes and models not to be square.
This Instructable will show an easy way to check a square accurately in a store before buying, and it will offer a surprise to consider when looking for a very accurate square.
Step 1: A little high school geometry
I had checked framing squares this way in two other stores, but had not thought to take a photo. These squares are shorter than a framing square. This particular store had only one framing square on the rack, so I chose to test these shorter squares. The framing squares I checked in other stores all had a "V" gap, too; but, the gap on the squares shown here was the most severe.
One lesson learned is that squares off the rack in all price ranges may be accurate enough for framing houses with 2 x 4s, but those I checked are not good for precise work, like making furniture, without making adjustments with an anvil and a ball peen hammer. (This method for adjusting a square makes a dimple that brings the legs of the square nearer to each other or pushes them apart, depending on where the dimple is placed in the corner.)