Agree that definite quantity time durations should not be used for calendar calculations. Agree that `1 year` should not be equal to `1 'a'`, and so on for all definite quantity time durations above seconds. Propose that the literal time durations be called "calendar durations" and represented as UCUM units using annotations: `1 year` is represented with the UCUM `1 ' {year} '` `1 month` is represented with the UCUM `1 ' {month} '` `1 day` is represented with the UCUM `1 ' {day} ` `1 hour` is represented with the UCUM `1 ' {hour} '` `1 minute` is represented with the UCUM `1 ' {minute} '` `1 second` is represented with the UCUM `1 ' {second} '` Only the "second" is equal to the UCUM time unit 's' Equivalent returns true, i.e. `1 year ~ 1 'a'` is true Date/time arithmetic is an error for the UCUM time units above second, only supported for the annotated calendar durations above second. on the grounds that it's too easy to mistakenly use UCUM time units and think they are calendar durations. Still note that calendar duration date/time arithmetic above seconds truncates (ignores decimals) Date/time arithmetic with seconds includes decimals, so users that really want `+ 1 'a'` to mean + 365.25 days, can convert the days to seconds and perform the operation that way. dateTime + 1 'h' // error dateTime + (1 'h').toQuantity('s')