If I have a person sawing a log for me and it takes them three quarters of an hour to saw through three quarters of a log I can reasonably assume that it will take an hour to finish the job. Given this information I can also assume that if there are ten logs that require sawing and one is done each day (so the person sawing is fresh each time) then each day I need to allocate one hour to the sawing task.
How can we software engineers explain to our managers that software development is not like sawing a log?
Firstly it’s exceedingly hard to know how far through the software you are at a given time.
Secondly you can’t usually predict when the next time consuming challenge is going to hit you. Some parts of a design may go smoothly but then the development may uncover something that had not previously been considered and the sensible engineering solution may well be to re-write (or at least refactor) some of the earlier design that may have been considered “finished”.
With larger projects this unpredictably does tend to even out so that you can (with experience) make estimates of the time needed to get a software system to a point where it is useable.
But I’ve just been asked how long will it take me to fix an issue with a particular type of output on a particular type of device. Once I find how to make the change it will be a ten minute fix. But how can I estimate how long it will take to find (or even if it is actually possible?). How much of the device manual will I have to read and understand in order to find the correct method to achieve the result ? And how much of the code will need to be redesigned to accommodate the required change(s)? And if the documentation is poor (as it usually is) how much experimenting / testing will be required to get it working?
So what do I do ? Quote a short delivery time and then look a fool (and perhaps upset the customer’s planned schedule) if it takes three times as long as I said ? or quote a long delivery time and get the reaction “how long? just to do that simple job! ”. Best is to try to get managers to read and consider this blog !