Video – 3, 4, 5 principle
The video shows a builder marking out a right angle on a building site using the 3, 4, 5 principle. First two pegs are placed four metres apart. Two tape measures are used from each peg. A third peg is place where the three and five metre points of the tapes intersect.
The audio for the video is as follows:
'We often have the need to set out a building and make sure that when we do set it out that it's square, tiles and kitchens everything like that, based on the principle that the building is going to be square.
To get it square we'll use a method called 3, 4, 5, and now I'm going to give you a demonstration how to set up a 3, 4, 5 triangle.
Ok so what I've put down here first of all is put a peg in at the desired point, and then I've come along and measured the second point 4 m along and put another peg in over here.
From there we're going to run a string line along that 4 m line.
Ok. So we've got a line here 4 m, and now we need to make a line out this way 3 m, and at the same time we want to make another line, the hypotenuse, that goes from that point out 5 m and join the two together.
So we've got 3 m. What have we got there?
Ok, so we've come along that line 3 m and we've come of the other point 5 m, if we line those two points up that will be exactly a right angle triangle.So now were going to extend our line along the 3 m line, ok, and tie it off down here.
Ok, so what we have now is one side that's 4 m long, we got the other side 3 m long, and the third side is now 5 m long.
If we wanted to check out to see if our triangle is square, we can come on over and use a builder's square and see that it actually is. So, placing it down, running it to one side, we can see that the other side's square as well.'