The amount shown on the scale of an instrument is called the reading.

Here's why:

* Reading implies the process of observing and interpreting the value indicated by the instrument's scale.

* Scale refers to the graduated markings on the instrument that represent different values.

* Instrument is the device itself, like a thermometer, a ruler, or a weighing scale.

So, when you look at an instrument, you are "reading" the value indicated by the scale.