### ECH_PRISMPOS

Determine the optimal prism rotation and position

##### Description

Determine the prism rotation and position by direct calculation. The rotation is such that a ray of the specified wavelength will fall on the centre of the detector. The position is such that the echelle is fully illuminated by rays of the specified wavelength.

ECH_INIT must be called before calling this routine.

##### Invocation

CALLECH_PRISMPOS (WC, GAMMA, POS, STATUS)

##### Arguments
 READ WC REAL Desired central wavelength (Angstroms) WRITE GAMMA REAL Optimal prism rotation (radians) WRITE POS REAL Optimal prism position (mm) READ, WRITE STATUS INTEGER Global status value

None known.

##### Authors

C.J. Hirst UCL (ZUVAD::CJH)