The documentations shows how to implement a basic VOL function:

```
Function VOL(a, b, c)
VOL = a*b*c
End Function
```

So that I can write

```
=VOL(1,2,3)
```

in a spreadsheet and get 6.

I want to write `arctan`

which would return result in degrees instead of radians:

```
Function ARCTAN(rad)
ARCTAN = ATAN(rad)*180/PI()
End Function
```

and call it as, e.g.:

```
=ARCTAN(1)
```

This doesn’t work: Calc complains:

Sub-procedure or function procedure not defined

Can you help me to write this function?