## Tip 16. User’s units of physical values

### Fig. 16. User’s units of physical values

There are predefined variables in Mathcad, which keep built-in units of physical values in different systems (see the sketch «Mathcad and physical values» (http://twt.mpei.ac.ru/ochkov/Units/unit.htm), as well as one of the books of the given series – «Physical values in Mathcad»). But user has the right to extend this list and to introduce into calculation user's units (see fig. 16), which are connected with built-in ones via corresponding coefficients[1].

At the beginning of a calculation user is not able to know what new units will be necessary. They can be introduced into the calculation as required: for example, it is necessary to output time in weeks – it is enough to come back to beginning of the calculation and to write week:=7 day and etc.

(exactly like this: 7 day, but not 7day – see tip 9).

The operator ì := m is handily in one more case. It is possible to fall into a reverie and to assign the variable m (but it is very popular) some new value (see tip 1) in a calculation. This operation is able to break all harmonious system of physical values laid in Mathcad. But the operator ì := m releases the variable m for keeping something else.

We could find the continuation of the theme in the sketch «Mathcad and physical values» (http://twt.mpei.ac.ru/ochkov/Units/unit.htm).

[1] How to work with degree Celsius, which can not be introduced via the conversion factor in a calculation – see tip 64.