Quality Control
Most colour measurement in the printing industry is done with that remarkable instrument called the eye. Remarkable as it is, the eye has its limitations as a device for accurately describing a particular colour. No two eyes are the same, so it may be that a printer and his customer do not see 'eye to eye' over the colour of a job.
Exact measurement means facts and not opinions expressed on what you think you see. This is the background to the efforts which have been made to develop instruments which could 'look at a colour' and describe it in figures.
The final printed impression is what is bought and sold. It is the quality of this that finally matters. The final printed impression is dependent on the colour separations and plates to produce good quality printing.