# Using Measurements¶

Measurements are the combination of two quantities: the mean value and the error (or uncertainty). The easiest ways to generate a measurement object is from a quantity using the plus_minus operator.

```
>>> import numpy as np
>>> from pint import UnitRegistry
>>> ureg = UnitRegistry()
>>> book_length = (20. * ureg.centimeter).plus_minus(2.)
>>> print(book_length)
(20.0 +/- 2.0) centimeter
```

You can inspect the mean value, the absolute error and the relative error:

```
>>> print(book_length.value)
20.0 centimeter
>>> print(book_length.error)
2.0 centimeter
>>> print(book_length.rel)
0.1
```

You can also create a Measurement object giving the relative error:

```
>>> book_length = (20. * ureg.centimeter).plus_minus(.1, relative=True)
>>> print(book_length)
(20.0 +/- 2.0) centimeter
```

Measurements support the same formatting codes as Quantity. For example, to pretty print a measurement with 2 decimal positions:

```
>>> print('{:.02fP}'.format(book_length))
(20.00 ± 2.00) centimeter
```

Mathematical operations with Measurements, return new measurements following the Propagation of uncertainty rules.

```
>>> print(2 * book_length)
(40.0 +/- 4.0) centimeter
>>> width = (10 * ureg.centimeter).plus_minus(1)
>>> print('{:.02f}'.format(book_length + width))
(30.00 +/- 2.24) centimeter
```

Note

only linear combinations are currently supported.