The high degree of accuracy maintained during production
ensures a standard path length tolerance of +/- 0.01mm. The tolerance
maintained for parallelism of the windows is better than 3 minutes
of arc, therefore Quartz cells vary little in transmission values.
Slight differences in the transmission of new Glass cells are due
to variations in raw material transmission characteristics.
The transmission of matched cells is measured and
each cell is given a match code. These codes are only of real value
when comparing new cells because the transmission characteristics
may change as surface contamination or deterioration due to handling
takes place. Thus a new cell of a particular match code will not
necessarily match an older cell of the same match code.
Although cells which are commonly used, such as
the standard rectangular type, especially in quartz materials, can
usually be supplied from stock in unlimited quantities of the same
match code, cells would normally be supplied in matched sets of
two or four, or in the case of Tablet Dissolution cells, matched
sets of six, seven or eight.