Dot Calibration of the 361T

How to calibrate the 361T for DotDot Area Calibration - 361T

This page outlines the "DOT" calibration routine which enables the user to alter the 'N-Factor' which controls all dot area calculations. In general, 'N-Factor' is always a number very close to 1.00. On occasion this number is altered by accident; the results are some pretty screwy dot measurements. X-Rite sets the 'N-Factor' at the factory for each 361T that is built. To reset the value, you will need a calibrated 50% screen (not supplied by X-Rite) or a piece of continuous tone film with an absolute density of 0.301 (equals 50% transmittance). Before performing a dot calibration, ensure that the Density Mode is properly calibrated. Only after this is done, perform a full dot calibration as follows:

With a Calibrated 50% Screen Film

  1. The word "CAL" is printed on the 361T. It is located between the "FUNCTION" and "COLOR" keys at the rear of the measurement arm. To begin the calibration routine, press both of these keys at the same time - then release.

     

  2. The unit will prompt "N Dcal Y". This prompt is for the density calibration which should have already been performed. Thus to continue, press the "FUNCTION" key to answer "N".

     

  3. The unit will display "N %cal Y". Here we want to answer the question "Y" and use the "ZERO" to do so.

     

  4. The densitometer will prompt you to "RdBase" (Read the Base material). If you are using an UGRA scale, locate the 0.5% dot as the base, else locate an area where there is no dot coverage (no image). Press down firmly as you read this area.

     

  5. The densitometer will next prompt "Read 50%". Locate the calibrated 50% target beneath the instrument's aperture and press down firmly until a number appears.

Dot% Calibration Complete

Note: If you do not have a calibrated 50% screen, It is best to reset the 'N-Factor' to 1.00. This can be done at step #5 (above).

Without a Calibrated 50% Screen Film

 

  1. When the unit prompts "Read 50%", press the "COLOR" key one time.
  2. The currently stored 'N-Factor' will be displayed; Note what filter is being displayed (Ortho or UV).
  3. Press and hold the "ZERO" key down then press the "COLOR" key to raise the value, or press the "FUNCTION" key to lower the value until the value in the display equals 1.00.
  4. Release the "ZERO" key then press the "COLOR" to change filters from Ortho or UV or from UV to Ortho.
  5. Press and hold the "ZERO" key down then press the "COLOR" key to raise the value, or press the "FUNCTION" key to lower the value until the value in the display equals 1.00.
  6. When done, release the "ZERO" and press the "FUNCTION" key to exit.

Note: Densitometers do not truly measure dot percentage. Instead dot percent is derived from density via the Yule/Neilson equation. Mathematically a density of 0.301 is almost exactly 50% opaque. Thus even in the absence of a certified 50% calibration screen it is still possible to reset the 'N-Factor'. If a film of this specification is used, measure AIR at the "RdBase" prompt.

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