Precision[expr]Note that the result could be slightly different than the obtained in WMA, due to differences in the internal representation of the real numbers.
The precision of an exact number, e.g., an Integer, is Infinity:
Precision[1]
A fraction is an exact number too, so its Precision is Infinity:
Precision[1/2]
Numbers entered in the form digits`p are taken to have precision p:
Precision[1.23`10]
Precision of a machine‐precision number is MachinePrecision:
Precision[0.5]
In compound expressions, the Precision is fixed by the number with the lowest Precision:
Precision[{{1, 1.`},{1.`5, 1.`10}}]
In general, Accuracy[z] == Precision[z] + Log[z] for non-zero Real values:
(Accuracy[z] == Precision[z] + Log[z])/.z-> 37.`
Following WMA, values in Machine Real representation starting with 0. are values are special:
Precision[0.]
On the other hand, for a Precision Real with fixed accuracy, the precision is evaluated to 0.:
Precision[0.``3]
See also Accuracy.