This is the context : "For most projectors however, including SONY projectors that have been used for a few months, or more and the bulb has aged, there is not a good reference for use in calibrating the test apparatus."

What does this sentence mean? Thank you for your help.

  • the act of calibration involves accounting for the measured difference between the actual outputs of the device being calibrated compared to the expected output given a known input. This known input is called a reference signal.
    – Jim
    Jan 25 '15 at 22:12

A reference in this kind of context is a fixed standard that is used to calibrate a piece of equipment or define a parameter. For instance, Pantone colours, the pitch of the musical note A, the Celsius temperature scale, the length of a second and the speed of light are all defined in terms of their relationship to a fixed value of some kind.

The sentence you quoted is saying that for projectors that are in the state described, for some reason no such standard value ('good reference') is available for calibrating the test apparatus.

Additional contextual information would be needed to fully clarify the situation.

  • Erik, Jim, thanks a lot for your answers, they definitely clarify the meaning.
    – FrenchMan
    Jan 26 '15 at 15:47

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