# PHI

The PHI function computes the third angle, in radians, of a body-2
Euler angle rotation sequence (body-3, body-1, body-3) of marker `I` with
respect to marker `J`.

## Format

PHI(I, J)## Arguments

`I`- The marker whose rotational displacement is to be computed. Must be specified.
`J`- The marker with respect to which the rotational displacement is to be computed. This argument is optional. If omitted, it defaults to the ground coordinate system.

## Example

```
<Post_Request
comment = "O_PSI_T_Phi"
id = "70000013"
type = "EXPRESSION"
expr1 = "NULL"
expr2 = "PSI(30102190)"
expr3 = "THETA(30102190)"
expr4 = "PHI(30102190)"
expr5 = "NULL"
expr6 = "NULL"
expr7 = "NULL"
expr8 = "NULL"
/>
```