Many pieces of wood have been ruined by not measuring accurately or too hastily. Sometimes when making a frame for a painting I forget to add the width of the molding when calculating the length to saw and thus the piece is useless.
This is extremely frustrating and causes much aggravation, especially if the molding is expensive and what is le ft is not enough to do it over. The whole idea is to measure, go back to the calculation to see if it was correctly done and measure again, so take your time.
The 3:4:5 Principle
When working with large boards, sometimes you have to cut a piece at exactly 90 degrees. If you only have a small square available, this can be a problem to extend the line to cut across the whole width of the board as some deviation is just about inevitable. This is where the following idea helps when marking out the job.
Now here is a tip. That is where the 3:4:5 principle can come in handy. It is based upon a mathematical equation such as 3 squared + 4 squared = 5 squared thus 9 + 16 = 25 where the corner across the 5 ft side of the triangle is exactly 90 degrees.
If the width of the board is 4 ft, you make a mark where the cut should be and make a mark 3 ft away from that one. Then you take a piece of string that has no give (it is not elastic). Measure 9 ft and cut it. Make a mark at the 5 ft measurement.
Clamp the two ends of string to the board at the abovementioned marks with small g-clamps. Now take the 5 ft mark on the string and make a mark on the board as it will then be exactly 4 ft (the width of the board) on the other side of the board and voila! you have the 90 degrees you wanted across the board.
This principle is used in many trades, for instance in road building or in the building trade when laying out foundations. The sides of the triangle can be in multiples of 3:4:5 ft, thus it can be 3 inches: 4 inches: 5 inches or 30 ft: 40 ft: 50 ft, it does not matter, the principle stays the same.
This could best be illustrated by a sketch but in this case a description has to suffice.
Accurate measurements are very important and cannot be over emphasized, but not only that, as it is essential that a project has to be thought through very carefully if you work out your own plans. Every detail has to be calculated carefully, taking into account the width or the thickness of your joining materials when working out the sizes that have to be cut, for the cutting list. A mistake here can ruin expensive pieces of wood if one uses exotic timber.
A good idea would be to have a friend check your dimensions as one is often unable to see a mistake yourself. I suppose every woodworker has had this experience in his work.