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For more details see Waveform model of data, Igor 5 Manual, volume II, p. 87.
Typically each data point in a wave corresponds to an experimental reading (value), which has been obtained at a particular time, distance, wavelength etc. - i.e. at some position in one of real-world dimensions. In many cases position is as important as value of the reading itself. Therefore, any set of values should have a set of corresponsing positions, which we call a calibration.
There are three ways to specify calibration in Igor:
- ordered postition in the wave
- scaled position
- separate calibration wave
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Ordered position is the simples way to indicate position and typically indicates inly the order in which values were recorded. Ordered position allways starts with 0 and increments by 1 from one point ot the next.
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When experimental values were obtaned at ordered and equidistant positions in a real-world dimension, such positions can be well described by setting wave scaling. Scaling specifies position of the first point and a change (or step) in the postition of each successive value. Examples of such calibration are:
- measurement taken every inch between one foot and two feet: start = 12, step = 1
- measurement taken every tree minutes from 20 to 41 minutes: start = 20, step = 3
Naturally, for scaled calibration it does not matter how many points were recorded.
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Most practical measurements are taken at somewhat random or predictable but variable intervals:
- time depended measurement are often progressively slowed later in the reaction
- wavelength reading of spectrometer depends on the angle between grating and the beam and therefore changes trigonometrically.
In such cases position must be specified by a calibration wave.
Calibration waves are no different than data waves, they simply store values from different dimension.
Common sense dictates that number
of entries in calibration wave must equal the number of entries in data wave.
Calibration waves can often be shared between data waves. Calibrations that typically can be shared:
- spectral data from fixed calibration spectrometer (HPSpec, OceanOptics)
- UV-VIS data obtained at the same monochormator configuration (TRIAX)
- Raman data measured between re-alignments
Time-based calibrations typically should NOT be shared. Even when controlled by a computer, time-based measurements usually occur at somewhat different times.
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