dave you should be ashamed at the very suggestion, i havnt yet found an accurate saw that has a square edge . Possibly the edge of a cereal box might give you a better reading. lol

no in all seriousness, the answer of getting one reading (whether its a square or level) and the flipping it round to see if it reads the same way, is the easiest and most accurate way of checking if either are true.

To get a right angle, I tend to use a roofing square unless it is over a larger area, in which case I often use a sheet of plasterboard ,or other sheet material which I usually have to hand. For much larger areas I use a tape measure and Pythagoras theorem

For levels, I check the vertical against a plumb line. Horizontal, I check against another level I have which I can prove is accurate because it reads the same when reversed.

It's more or less conclusive then, that for No2....trueness of a right angle....it's the 3,4,5 rule.

I like the 'floating the spirit level in the bath' for No1.....Accuracy of a spirit level.

I did come up with another potential or two for Q No2....

Hang the level from a nail (if your level has a centre hole at either end) so that it hangs freely, or loop some string through it and hang it like a plumb bob.

I guess doing this would work for checking the vertical bubble, and the 'water'' methods for the horizontal bubble.

well...here's the result!

1st place goes to....(drum role)........JoinerJohn.


Thanks for taking the time to respond chaps....quite good for the brain matter and curiosity factor.

It did prompt me to look up 'how the ancients measured angles and levels'.....

The Egyptian Groma, and the Greek Dioptra.