<< It might not be very easy to say what causes the discrepency between the
plot and the measured density. Basically one take rseadings at certain
interval and then interpolate the data. You don't really know how good of bad
the interpolation is. There are many ways of interpolations: B-Spline, cubic
spline, or least-square approximation if the physical property is known.
Depending on the algorithm and the physical property, the data might or might
not match the actual data if measurement is made. Most densitometer has an
accuracy and repeatability of 0.01, so if your densitometer is still
functioning properly, the difference might not be caused by it.
Some asks why one would need to use a software to plot data, I think like
anything that use computer, if you have the proper setup, it might work
faster for you (it really depends on the setup though). For example, the
X-Rite densitometer can send data directly to a computer, so if I connect the
densitometer to my computer, I can probably take readings in about a minute,
and hit a few buttons on my computer, and get a characteristic curve.
It is fast, but like I said, the curve is just an interpolation of the
measured data. I can't even say that it is better than manual plot, so I
don't even use this setup for my photographic application.
In my research work in color calibration, however, I need to read about 144
color patches and do calculation on the data. Since I need to know that I
don't make mistake when I read the data, I read about 50 reading for each
patch, then check the statistics to make sure that the data is
correct/reasonable. Since each color has 3 value (R, G, and B), I have
144*50*3 = 21600 numbers for each pass. You can imagine how difficult it
could be even to write down the numbers manually!
>>