calculators for travel - some ideas

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calculators for travel - some ideas

I tend to work a lot in airplanes and hotel rooms with poor lighting. Some of my colleagues only use computers, retorting to Excel when they wan to perform any calculation. When you perform financial analysis, it’s very comfortable to use the excel spreadsheet. However, when you’re working from written information, a calculator and a pencil has some advantages.

But the problem in most of cases is the poor lightning condition in many of the places we spend our time. And the typical calculator you have doesn’t help, because the screen is not illuminated.

You have then two main options: use a calculator app for your iPad or mobile phone (an option we’ll discuss in a moment) or use a backlight calculator. And there, your only option is the hp Prime!

The challenge with the HP Prime is that it is a fantastic student calculator. It is not a financial calculator, by any means! (Well, it has the finance (TVM) app). But, as it is programmable, something can be done about it.

So far, we’ve created NPV and IRR functions that can be used in any occasion. Also, it makes sense to remap the calculator keyboard with some other useful functions: %, %CHANGE and %TOTAL. In my case, I have assigned these to the unsigned sin(), cos() and tan() keys.

The latest firmware revision brought a number of time calculations, that have always been useful in financial settings: DDAYS, DATEADD and DAYOFWEEK come to mind in the first place. The reason I put these among financial functions is that when you’re preparing an investment, date operations tend to appear:“we’ll do first this payment, and then we will cancel it that many days later with another payment, so that makes X days of interest”, etc.So these are as well candidates to replace other keys in the configurable keyboards.

I have assigned these to the LN and LOG keys.

Although many of you know how to assign a key to a function in the hp Prime calculator, some still don’t, so it is worthwhile to explain it.

The syntax is very easy, and, as said before, it can be launched from a template, as seen on the picture beside. I use a lot of percentage comparisons, and, on the other hand, very few trigonometric functions, so I mapped all three typical percentage functions (already existing in the Prime) to the three trigonometric keys, on their main unshifted meaning:

screenshot.29KEY K_Sin()




KEY K_Cos()




KEY K_Tan()




What does it does? It writes at the cursor position the text between inverted commas. It does not separate it from the previous number, but we’ll see shortly after that it does not matter.

Note that if you want to reprogram shifted keys, you may do it as well, by changing the key prefix:

K_ stands for main key

KS_ is for shifted keys

KA_ is for alphanumeric

KSA_ is for shifted alphanumeric

The coding of each particular key is shown in page 518 of the manual. (The full manual can be shown in the Windows Prime emulator, in the help menu)

Please contact me if in your work you need different functions at

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