I only use Wyeast Smack Packs and I always make starters and have been ever since I got into this hobby. I have always used Yeastcalc for my calculations and have noticed the last several times that there are now two stir plate calculators- one is Jamil's and the other is Troester and they calculate differently. So out of curiosity I also visited MrMalty and used the slider to make the growth factor the same as the two represented on Yeast calc and am looking for some continuity and not finding it. I'm hoping someone can give me an explanation as to where the differences are coming from.

Example:

Package date: 3/13/2013

Viability: Yeastcalc-81%, Mr. Malty 69%

Batch size: 6.25g

Og: 1.054

YeastCalc

Stir Plate: Jamil-growth factor 2.01 requires 244B cells, 1.5L starter

Stir Plate: Troester-growth factor 2.6, 292B cells, 1.5 L starter

MrMalty:

Stir Plate: 236B cells, 1L starter-sliding of growth factor made no changes

I realize, on average the difference in cells is not huge and all of my beer as attenuated well with no issues and I have always used Yeastcalc as I like the ability to calculate stepped starters so easily and I am not losing sleep over this but my curiosity has been peaked so my inquiring mind wants to know if one is more accurate than another and why the differences?