Hrair limit
Hrair limit, a term borrowed from cognitive psychology, was used by Ed Yourdan in his Modern Structured Analysis (Prentice Hall, 1979) to mean the maximum number of subroutines that should be called from the main program. It is a number betweeen 5 and 9. The limit is not there because the computer will become confused if it is exceeded, but because the programmer will.The concept of the hrair limit is illustrated by imagining the six faces of a die used to play dice. It is easy for many people to visualise each of the six faces. Now imagine seven dots, eight dots, nine dots, ten dots, and so on. At some point it becomes impossible to visualise the dots as a single pattern, and one thinks of, say, eight as two groups of four. The upper limit of your visualisation of a number represented as dots is your hrair limit for that exercise.
In organisation theory the term has a similar meaning: the maximum number of projects that one can be involved in simultaneously before chaos starts to ensue.
It is particularly advantageous for computer programmers to have a high hrair limit because their effectiveness is enhanced if they don't get confused too often. Each time a programmer gets confused, either through grappling with a problem that has not been adequately analysed to take account of the programmer's typical hrair limit, or even due to a simple interruption like answering the phone, it has been estimated (by Gerry Weinberg) to cost the project on which the programmer is engaged at least half an hour of lost time.
The film Rain Man, starring Dustin Hoffman, portrayed a fictitious autistic savant, who was able to visualise the number represented by an entire box of matches spilled on the floor. A similar feat was clinically observed by psychoneurologist Oliver Sacks and reported in his book The Man Who Mistook His Wife For A Hat. Therefore one might suppose that the hrair limit is an arbitrary limit imposed by our cognition rather than necessarily being a physical limit.