Spring time is a great time to start a vegitable garden, when laying one out it looks good if the boarders are at 90 degrees to each other, with this beer can set square this is easily done. It has other uses such as laying out a shed or concreate slab.
Making it uses no power tools and is quite simple to do.

Supplies

Beer Can (or other aluminum beverage can)
String
3 pegs
Marker pen
Scissors

Step 1: Make a Mark on an Aluminum Can

Make a vertical mark on a beer can.
Place a piece of string on the can and mark it at the previously made mark.

Step 2: Wrap 3 Turns

Wrap 3 turns of string around the can and then mark the last wrap of string at the mark on the can.

Step 3: Wrap 4 Turns

Starting at the mark just made, wrap 4 further turns around the can, mark at the 4th turn.

Step 4: Wrap 5 Turns

Starting at the mark just made, wrap another 5 turns around the can and mark the string at the 5th turn.

Step 5: Tie Ends Together

Taking the string off the can, cut it about 4 inches after the last mark made. Tie the string together joining it at the 1st and last mark, so it forms a loop.

Step 6: Take It Out Into the Field for Testing

Wrap the loop of string, with the marks you have made around the can, place 3 tent pegs in it and take it to the location you want to lay out a garden or other project.

Step 7: Using the Square

Unwrap the loop of string from the can.
Peg in one of the tent pegs where the string has been tied and move it along one of the edges you want to make untill you come to another mark on the string. peg in a second peg. Do the same process for the 3rd peg at the 3rd mark. the string needs to be tight.

You will have made a right angle triangle. Reposition if required.

To make a bigger set square, just increase all the wraps around the can be a constant factor, Eg, 6, 8.10 or ever 9, 12, 15. Increasing the size will also improve accuracy.