(6) Set Q1 and Q2 levers for the mercury 3129 A.U. wavelength using the instrument's Table
Settings of Q.
(7) Adjust instrument sensitivity so that the microammeter reads close to the maximum value
on the scale. (If a reversing switch is not built into the microammeter, it may be necessary
to reverse connections to the microammeter.) If the microammeter deflection is too great
with the sensitivity control set for minimum instrument sensitivity, the intensity of the light
entering the spectrophotometer may be decreased by placing one or two small pieces of
lens tissue paper over the ground quartz plate. Alternatively, a permanent light attenuator
may be installed within the Hg lamp housing. The microammeter deflection should not be
reduced by means of the microammeter shunt, since, if this is done, the amplifier may be
overloaded and no longer linear.
(8) Read and record the temperature of the instrument to the nearest 0.1 degree.
(9) Adjust Q1 to give maximum microammeter reading.
(10) Move the Q1 lever upward to reduce the microammeter reading to one-half the maximum
value. Read and record this value (upper half-power point) of Q1.