### 2 Routine Summary

The following routines are available. Refer to the next section for an overview of how they are used.

ECH_BLOCK:
BLOCKDATA to initialise spectrograph configuration COMMON block
ECH_COLLIMATOR:
Determine which collimator to use at a given wavelength
ECH_DISP:
Determine the dispersion in mm for a given wavelength in a given order at a specified configuration
ECH_FORMAT_CENTRE:
Determine the appropriate spectrograph settings to place a specified wavelength in a specified order at the centre of the field
ECH_FRSPR:
Determine the free spectral range in Angstroms of a specified order at a specified configuration
ECH_INIT:
Initialise COMMON blocks for a specified instrument combination
ECH_LOAD:
Load COMMON blocks describing spectrograph parameters
ECH_ORDERNUM:
Determine the order number of a specified wavelength at a specified configuration
ECH_PRISMPOS:
Determine the optimal prism rotation and position at a specified wavelength
ECH_REFINDEX:
Determine the refractive index of fused silica at a specified wavelength
ECH_SLITANGLE:
Determine the optimum slit angle at a specified configuration
ECH_WAVECEN:
Determine the central wavelength of the order nearest to the centre of the field at a specified configuration
ECH_WCENTRAL:
Determine the central wavelength in Angstroms in a specified order at a given configuration
ECH_XDISPFS:
Determine the cross-dispersion in mm for a given wavelength at a specified configuration