once per year versus three times a week? A Japanese friend told me that 週三回　is the way to express 'three times a week', and according to the dictionary, 年に一度　is the way to express 'once a year', but once a month, apparently is 毎月一回　so not surprisingly I am a bit confused - is their any rhyme or reason about how to express the frequency of occurrence at different intervals? So, once, twice, three times etc, per hour, day, week, month, year, etc.? Thank you - I do find Japanese numbers/counting one of the most difficult things about the language!