Harvesting yeast can be simple or it can be hard. Yeast rinsing/washing is the hard way. I did this the first few times harvesting. I would end up with only about 100 ml of yeast. Lot easier to use Brew United overbuild calculator for a starter than harvesting with the rinsing method. I am currently using the overbuild method to produce yeast for the next starter.
I still harvest just in case my starter overbuild yeast would get infected or somehow lost. I'm planning for the worst case scenario.
I had lost faith in Mrmalty because the viability calculator had never been tested by cell counting, but was interpolated as a linear progression of viability loss. According to Mrmalty a 3 month old Wyeast Smack pack would only have 10% viability. Brew United 50% viability. I went back and looked at Mrmalty this morning. It seems the calculations are logical if you manually enter the percent viability, as calculated in the Brew United calculator and adjust the sliders for the way your yeast looks.
I have had a few unusual fermentations. May be time to reevaluate my use of 2 billion yeast cells per ml. May be way to conservative. I'll have a new topic a little later to get your opinions. Might tile it, "Yeast krausen".