CalcPM grew out of my experience teaching physics to undergraduate students. An important part of any laboratory experiment is to evaluate measurement uncertainties (or errors - as used by some). During introductory laboratory experiments we expect students to be able to asses these uncertainties (which should never-ever be half the smallest division on the measurement device) and then combine them to come up with some meaningful result. While I would expect students to be able to make these calculations, I would not expect them to do repeated calculations by hand - hence the development of a calculator to facilitate this.
I first wrote a Java version of such a calculator around the year 2000.
This functioned well but required access to a web browser on a computer and
hence was not particularly portable. With the advent of smart phones and tablets, it became a hobby of mine
to develop my programming skills so that I could adapt the calculator for use with both iOS and Android.
The first version of CalcPM for iOS has been
completed and became available on the Apple App store in October 2012.
The Android version was subsequently released in January 2013.
Quick Start Guide
CalcPM operates exactly like a standard calculator but allows the association of an uncertainty
with each number in the calculation. The only major difference between a standard calculator and CalcPM
is the addition of an input for the uncertainty. The user swaps between inputting a number
and inputting an uncertainty by the use of the "--/--" button. An example calculation would be as follows
56 --/-- 3 x 22 --/-- 1 =
This gives an answer which is 1230 +/- 90 (to one significant figure in the uncertainty). Other functions are (hopefully) self-explanatory.
The same calculation can be performed in RPN mode (selected within the Settings panel) as
56 --/-- 3 Enter 22 --/-- 1 x
The free version, CalcPMLite, functions in the same way as the full version except that it is limited to standard mathematical operations (+,-,x,/). The full version includes a range of scientific functions, and can be operated in the standard BOMDAS mode and in reverse polish notation (RPN). A small charge is associated with the full version - I'm not expecting to get rich, simply trying to recover some of the charges Apple and Google inforce on me to be a developer.
The full version includes a special "Sum" operating mode. This allows for one touch summation of digits 1-9 as well as the numbers 10 and 0.5. I originally wrote this to assist with totalling exam marks - but it can be of use anyway where the quick summation of a set of numbers is required.
Calculations are performed based on the method of combining random uncertainties. Given a function, p, of the form
the uncertainty, Δp, is calculated by
Functions are calculated in a similar way. For example, given
The uncertainty is given by
where angles are given in radians.
The following settings are available