IMAGE. The meter on a Spectronic 20™ viewed such that parallax has been eliminated.
IMAGE. Note the reflection in the mirror and that a reading of 58.1 %T would be recorded. This value would be inaccurate due to the incorrect positioning when the reading was made.
The Two Scales: The Spectronic 20™ meter displays both absorbance and % transmittance. Readings from the meter should always be taken from the % transmittance scale since it is more difficult to estimate between the graduation marks on the logarithmic, absorbance scale. Percent Transmittance can be converted to absorbance using the following relationship:
A = -log (%T/100) = log 100 - log %T
The Mirror Behind the Needle:
When looking at the meter, eliminate the reflection of the needle in the mirror. When the reflection is eliminated, the viewer is directly in front of the meter and parallax has been eliminated. Correct and incorrect views of the meter are shown.
