Figure of Usability calculator
This is my attempt to put some mathematical sense to Fugure of Usability.
C is a coefficient, which combine describes frequency and time of usage. For example if you used your VCR only 2 times a year C=0.01, where your wrist watch constantly hanging on your wrist would have C=1.
C can be estimated by following formula C=(Tu*N)/T where N-numbers of usages over life time T and Tu- is the period of time used in each usage. VCR used ones a year for 1 hour with 5 years of life time would give us 5*1/8760hr= 5.7e-4
T- is time of total usability until discarded. Another words T is the lifetime of the product.
The simplified formula would be as follows: U=(K*T*C)/(M+Mr)
Where U – is mentioned above normalized merit of usability (number that represent usefulness of an item). M- your money spent for initial purchase. K- subjective coefficient of usability. For example plasma TV can have about K=0.5 superficial usability compared to laptop with K=1. Argument is that the laptop can be used as TV to watch a movie, but TV can’t be used as a laptop. Mr=money spent for repairs.
K is very superficial number between 0 and 1. It can be obtain via statistics pole as well as with common sense perception. To simplify things we define K=Pw+Pu/Pu where Pw People wished to use it and Pu- people used it.