The precision of a number is a similar concept to significant figures. For instance, if I was measuring the length of my hand, I might be able to measure it to the nearest millimetre and get a length of 18 mm. I would have measured my hand’s length to a precision of 1 mm.

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If I had more precise equipment, I might be able to measure the length of my hand and get a length of 18.4 mm. In this case, the precision of my measurement would be 0.1 mm, not 1 mm.

Like for significant figures, there can be confusion about precision when you get a measurement like this:

300 m

Was this measurement precise to 100 metres or 1 metre? *Strictly
speaking*, since two zeroes have been written down in the ‘10’s and ‘1’s
part of the number, I would read this number as being 300 metres with a
precision of 1 metre.

Using scientific notation avoids this potential confusion.
If I wanted to tell the reader the measurement was 300 metres with a precision
of *100 metres*, I would write:

_{}

If I wanted to tell the reader I meant 300 metres with a
precision of *1 metre* I’d write:

_{}

Precision can also be talked about in terms of significant
figures. For instance, _{} is precise to three significant
figures, whereas _{} is only precise to one significant
figure.