For a picture of an Digital Spectronic 20D+ see below.

1. TURN THE INSTRUMENT ON

Turn the lower front left control knob clockwise. The red LED display should light up or the red indicator light should come on. If the light does not come on, check to make sure the instrument is plugged in.

2. ALLOW THE INSTRUMENT TO WARM UP FOR 15 MINUTES.

3. SET THE DESIRED WAVELENGTH.

The wavelength control is the knob on top of the instrument to the right of the sample chamber.

4. SET THE ZERO CONTROL.

Open the sample chamber and ensure that it is empty. If the instrument has a digital display (LED), set the instrument to Transmittance mode (T) using the metal switch located near the LED. If it has an analog display, just make sure you are reading the Transmittance scale for the next command. Close the sample chamber cover and turn the lower front left control knob until a reading of 0.0 is obtained on the Transmittance scale. Do not adjust this knob again throughout the experiment!

5. SET THE ZERO BLANK.

Open the sample chamber and place the cuvette containing the blank into the instrument. Be sure to gently wipe the cuvette with a KimWipe to remove fingerprints before inserting it into the Spec 20. DO NOT use ordinary test tubes. Push the cuvette down gently until you hear an audible "click". Close the sample chamber. If using a digital Spec 20, make sure you flip the switch to the Absorbance mode (A). If using an analog Spec 20, make sure you read the Absorbance scale. Using the front lower right knob, adjust the display until it reads 0.0 absorbance units.

6. REMOVE THE BLANK.

7. INSERT THE DESIRED SAMPLE FOR MEASUREMENT.

Make sure that there are no fingerprints on the tube and place the sample into the chamber as before. Close the sample chamber lid and the read the Absorbance from the display. Make sure you record the value to the furthest place after the decimal as possible. For example, on the analog Spec 20's you can estimate to the nearest 0.001 Absorbance Units.

8. PERIODICALLY READ THE BLANK AND READJUST (STEP 5),
IF NECESSARY, TO ELIMINATE PROBLEMS OF INSTRUMENT DRIFT.