<I think you are spot on there, I am led to believe the 60hz decision in th <US and some other countries was made to facilitate the use of the <(relatively) precise mains frequency for clocks and other timing functions <This is also possible, even for motor driven clocks, with 50hz mains simpl <by careful motor design. Though it may have been less simple when the <decision was made. makes no difference save for one item... <equivalent to the mains frequency. This reduces/eliminates mains hum <strobing, though it is more of a historical problem with modern TV designs <think. No, more of a problem with OLD designs. The key item is that motors and transformers are physically smaller for same or similar VA capability with increasing frequency. there is a corner you turn as you go higher though as the iron in the course gets lossier and line radiation increses losses. So power distrubution has the 50/60 as a good bet. Note aircraft use 400nz for the compact transformers and reduced filtering in rectifiec circuits. There were also 25, 30 and 40hz systems. The NY subway at one time was 25Hz and the DEC mill prior to refurb in the 80s was 40hz (that power also lighted part of the town.) at one point in history. Allison