The widely used Beckman DK2 (DK2A) recording
spectrophotometer has no such scaleexpansion
facility. The commercially available
scale-expansion unit for the Beckman DB instrument
expands the percentage-transmission scale,
not the extinction scale, and does not solve the
problem for the following reason. Chemical changes
are proportional to extinction changes, not to
transmission changes. The multiplication of the
percentage transmission by a constant factor is
merely equivalent to the addition of a constant
quantity to the extinction; a tenfold expansion of
the percentage-transmission scale is equivalent to
the addition of 1 to the extinction scale, and this
leaves the slope of the time curve unaltered. In
any case, the Beckman DK2 instrument already
has provision for the addition of 1 to the extinction
scale.