On the front face of the machine is the “EYEPIECE” at the top. Below that is the “FINE ADJUST” dial; below that is the “PRISM” on which the sample is placed and in front of that is the moveable “LIGHT” source. The “POWER” toggle switch is located on the left side of the instrument.

On the right hand side of the machine is the “COARSE ADJUST” knob and the “THERMOMETER” in the metal casing.

3. Place 2-3 drops of sample onto the bottom PRISM using a clean pipette, making sure that you do not touch the PRISM with the pipette.

4. Close the PRISM and swing the LIGHT up against the prism until the light stops.

6. Turn the COARSE ADJUST knob until the light/dark interface is located approximately at the crosshairs.

7. If you are observing a rainbow of colours, turn the FINE ADJUST knob until a sharp interface is obtained.

8. Turn the COARSE ADJUST knob this time until the interface is right at the crosshairs. If you are having any difficulties making these adjustments or seeing uneven interfaces or blobs of black colour, that is probably because you don’t have enough sample on the PRISM.

9. Hold the POWER switch down to view the scale and read your R.I. where the vertical line crosses the top scale, to 4 decimal places (the 4th decimal place is estimated). The bottom scale is not used here.

10. Record the temperature on the THERMOMETER to 1 decimal place.

11. Open the prism and wipe the upper and lower plates with a tissue moistened with acetone. Leave open to dry.