The PRR is only a useful measure for companies which engage in a substantial amount of research and development expenditure every year. It can be a useful measure of value when companies are making losses or insignificant profits. A low PRR can indicate that a very substantial amount is being spent on research in relation to the share price and that, in these terms alone, the shares are a bargain.

The second and third columns have been devoted to PSR and the trend of sales because the PRR and PSR often work in conjunction with each other. The fourth and fifth columns have been used for margins and the trend of margins and the last two for PCF and prospective PER.

An important caveat on PRRs is that the allocation of research expenditure can be somewhat arbitrary; different companies may classify the same expenditure in different ways.