- 24 Aug 2008
- Reaction score
- Essex/ Suffolk border
I like this image to demonstrate it:No, it's not. What he is saying is that if a drawing requires 4 frame pieces at 320mm, if he makes 4 at 321mm then he has precision but not accuracy. The frame will fit as the accuracy error is the same on all components.
That’s it, I made a set of jenga blocks recently that are also a great example, having them precise is critical, but the only accuracy really important is that the width is 1/3rd the length, the rest is all precision
This graphically shows what I said earlier. Absolute accuracy is not important, relative accuracy is. If one chooses to use Precision instead of Relative Accuracy that's fine by me.
YES! Especially with a tape measure. In addition to the uncertain behaviour of the hook at the end, the printed-scale process for tape measures is prone to some systematic errors (for example, slight eccentricity of the disc doing the printing). If you buy a tape measure, ensure that it is rated as Class I (a small symbol printed near the start of the tape). Some unclassed ones can be better but you have to calibrate them to know! In general, engraved steel rules are better.This might be the most basic of basic but while a measurement instrument might not be the most accurate, it will be consistent; always use the same one for the whole project
Precision is the correct name for that quantity. If you use non-standard terminology you're just going to confuse people.This graphically shows what I said earlier. Absolute accuracy is not important, relative accuracy is. If one chooses to use Precision instead of Relative Accuracy that's fine by me.
And there I thought I was the only one doing this!If I'm using a tape measure for accurately marked measurements I draw the tape out and place the 100mm line (or 1" if you're old school) where I need to measure from and then mark the measurement +100mm, so say if I'm wanting to mark 821mm on a piece of timber using this method I would have to mark it at 921mm on the tape to account for the 100mm at the front end.