Whenever I design a presentation, I almost always have a calculator open on my desk. I design all my data charts by hand, the old fashioned way, doing the final step completely analogue to make sure that resulting slide is really the very best to convey the specific message I want to get across. The calculator is used to calculate the % breakdowns, and to do the final check whether the whole thing adds up. Small calculation errors can distract the audience and undermine the credibility of your analytical work. (I she cannot get the numbers in the chart to add up, what about the underlying spreadsheets?)

So, over the past decades I have used the famous

**HP 12C**as my sole calculator. First in hardware form, then as an

**app on my iPhone**. Since spreadsheets arrived in the early 1990s, I have no need anymore for sophisticated NPV calculations on a calculator. I was simply used to the user interface of the machine, to such an extend that I replaced it for about EUR 100 with a new one a few years ago.

The iPhone HP 12C works, but is not perfectly convenient. I always fiddle with the landscape-only orientation, and the buttons are a bit too small to be convenient. So the iPad solves at the least the button size issue. Like note taking apps, there are an infinite amount of calculator apps available for the iPad (including the build in one).

I found only one that has an absolutely essential feature for the paperless creative workflow: a small electronic piece of paper to scribble notes. Hence, my preference goes out to

**Calculator HD for iPad**. Just a shame that it does not have the

**Polish notation**I got used to on my HP 12C...

A more serious shortcoming though is the inability to work with powers of ten in the basic note pad model. It is hard to tell those billions and millions apart. Does anyone have a better recommendation?