Grams to Krebs conversion formulae

After many a day scratching my head as to why I can’t get my viscometer to calibrate correctly, even assuming logarithmic and quadratic relationships, I find out why I have been having so many problems.

Krebs units are in not very linear!

I have found an old chart with lots of grams to krebs conversions on it and after painstakingly transcribing them, I have come up with the following graph.


Grams to Krebs (grams on horizontal axis, krebs vertical)
Grams to Krebs (grams on horizontal axis, krebs vertical)

As you can see, there are a number of points of inflection along this graph. Here are some images of the various best fit scenarios regarding this set of points. These points encompass the KU values 40.1 to 141, just for reference.

Linear (0.0813637)*x+(64.5289)
Linear (0.0813637)*x+(64.5289)

Quadratic (-0.0000813007)*x^2+(0.173302)*x+(46.274)
Quadratic (-0.0000813007)*x^2+(0.173302)*x+(46.274)

Cubic (1.01193e-7)*x^3+(-0.000252971)*x^2+(0.253045)*x+(37.7895)
Cubic (1.01193e-7)*x^3+(-0.000252971)*x^2+(0.253045)*x+(37.7895)

Quartic (-2.3958e-10)*x^4+(6.42986e-7)*x^3+(-0.000653817)*x^2+(0.359922)*x+(30.3868)
Quartic (-2.3958e-10)*x^4+(6.42986e-7)*x^3+(-0.000653817)*x^2+(0.359922)*x+(30.3868)

Quintic (1.93677e-13)*x^5+(-7.87171e-10)*x^4+(1.20087e-6)*x^3+(-0.0008998)*x^2+(0.403747)*x+(28.1763)
Quintic (1.93677e-13)*x^5+(-7.87171e-10)*x^4+(1.20087e-6)*x^3+(-0.0008998)*x^2+(0.403747)*x+(28.1763)

As you can see, a quartic relationship is quite passable though I still added a quintic relationship. It may be possible to make a simpler equation based on these values but I thought it prudent to stick to what I know.

You can see the dataset here. GramsvsKrebs.txt

Be warned, I may have made mistakes or the chart may have been wrong, Do your own research if you want to be certain of your results. Hopefully this is of help to somebody.

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