A chemist needs to know the mass of a sample of to significant digits. He puts the sample on a digital scale. This is what the scale shows: 0
0
0
7
6
.
3
g
If this measurement is precise enough for the chemist, round it to significant digits.
Otherwise, press the "No solution" button.

76.3 g aka 76 g
In type of scientific measurement, the precision of the measurement is expressed in the significant digits of that measurement. It also used to express measurement to the required degree of accuracy.
Significant digits include every digit except the leading zero(s).
And if the number after the required significant digits is not up to 5, it is rounded down and the required significant digits is written as is. If the number after the required significant digits is at least 5, it is rounded up, and the last number on the significant digits requirement is increased by a factor of 1.

Idon't mean to be a smart alec, length of atoms' bonds is the simplest way to define it.