The Heiland is pre calibrated with all kind of different papers, developers and some different type of films with the necessary sensiometric data.
Offsets are corrections made on the default values in 1/10 of f-stops and 1/10 of grade. They will not influence the measurement with the probe.
Put on the focus light, darkroom light is automatically switched off, enlarger lens aperture full open, focus the negative, close the aperture 2-3 f stops, when you have chosen continuous mode on the Heiland move the probe slowly from the most light part through the negative to the darkest parts. Focus off, calculation logD has been made and converted with some sensiometric data from the chosen paper to the best fitted grade. Measurement should be possible in a wide range of light and grade.
Is your basic installment LPL4550 or so, when switching on the unit?