Fizeau–Foucault apparatus unit. At the time, Foucault was working at the Paris Observatory under Urbain le Verrier. It was le Verrier's belief, based on extensive celestial mechanics calculations, that the consensus value for the speed of light was perhaps 4% too high. Technical limitations prevented Foucault from separating mirrors R and M by more than about 20 meters. Despite this limited path length, Foucault was able to measure the displacement of the slit image (less than 1 mm) with considerable accuracy. In addition, unlike the case with Fizeau's experiment (which required gauging the rotation rate of an adjustable-speed toothed wheel), he could
Which? shops selling hearing aids and an investigation into electronics shop staffs' knowledge of the products that they sell. Other publications include "Which? Travel", "Which? Car", "Which? Money", "Which? Computing" and "Which? Gardening". The Consumer's Association has experienced sharply increased income in recent years as its trading subsidiaries have expanded their activities. Which? regularly briefs and lobbies MPs, Peers, AMs, MLAs, MSPs and MEPs on national, European and international consumer issues. For example, Which? successfully lobbied to put an end to the '65-day rule' that allowed energy companies to wait 65 days before informing their customers of a price change. Following