Nulling the instrument
Turn on the instrument; Allow approximately two minutes for the unit to stabilize.
Take a reading with no film (read air).
While holding the "READ" button... press and release the "NULL" button, the instrument display should reads 0.00.
A second reading should be taken with no film to verify that the unit is holding zero.
Calibrating / Setting the instrument's slope
Locate the Calibration Reference film and the small screwdriver.
Turn on and zero (null) the instrument as described above.
Measure the CAL step of the supplied film.
If the measurement differs from the certified strip value by more than ±0.02D use the small screwdriver to increase or decrease the unit's slope untill it agrees,
Again zero the unit... and follow by again reading the CAL step... repeat this zero/measure/cal/zero/measure sequence until the unit is accurately reporting the calibration density.
After adjusting to the cal step read the other 4 steps, they should fall into the +/-.02 tolerance if you have a linear unit.