### ECH_ORDERNUM

Determine the order number of a specified wavelength

##### Description

Use the grating equation to calculate the free spectral range and then derive the order number directly from it.

ECH_INIT must be called before calling this routine.

##### Invocation

CALLECH_ORDERNUM (W, THETA, GAMMA, M, STATUS)

##### Arguments
 READ W REAL Wavelength whose order number is to be determined (ie the order number within which it lies within the free spectral range) (Angstroms) READ THETA REAL Echelle theta angle corresponding to the current configuration (radians) READ GAMMA REAL Echelle gamma angle corresponding to the current configuration (radians) WRITE M INTEGER Order number corresponding to wavelength READ, WRITE STATUS INTEGER Global status value

None known.

##### Authors

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