Jon, thanks for digging that out - I saw that spreadsheet the other day when I was doing my 'day job', and the underlying considerations were conservative. Most folks will do better than the model, but everyone has experienced a "Giveaway Bob" wild numbers scenario, so I run numbers the way I was trained by corporate accountants.
The other day I needed to run some numbers at a checkout, and I got the number ahead of the cashier with the calculator or the helper with the mobilephone app. They were a bit 'weird-ed out', but I told them you learn out to do math in your head so you don't have to break out the slide-rule until you absolutely have to get it out. Don't think they know what a slide-rule looks like.
