How come different spectro devices from different brands give different density measurements, even different from Offset presses manufacturer measurement tools such as Manroland and Heidelber? What is the diffference based on?

How come different spectro devices from different brands give different density measurements, even different from Offset presses manufacturer measurement tools such as Manroland and Heidelberg? What is the diffference based on?

The differences can be caused by many reasons. The first thing to check is the measurement settings on different insturments. For example, the common density setting used in North America is ISO T/ No Polarization filter/ Absolute. Any change in the setting will greatly influence the measured results. Other thins we can check is the device condition, such as any damage to the device aperture, recertification/factory calibration validity, white tile condition and calibration interval.