Comment #5 on issue 3806 by cesar.ra...@gmail.com: Duration>>hours is broken http://code.google.com/p/pharo/issues/detail?id=3806 While I can second Sebastians' complains based in intuitivity, I got confused with the redaction of the ANSI standard, which I have only a 1.9 Draft in PDF form: 5.8.2.11 Message: hours Synopsis Answer the number of complete hours in the receiver. Definition: <Duration> Answer an <integer> between -23 and 23 inclusive that represents the number of complete hours in the receiver, after the number of complete days has been removed. If the receiver is less than <Duration factory> #zero then the result will be less than or equal to 0. Return Values <integer> unspecified Errors None This text seems to support the implementation of the method which is attempting to give the number of fractional part of the duration. It does not seem to be a conversion protocol, but rather an equivalent to the mod operation for hours, or seconds or whatever. Test this: (DateAndTime now - DateAndTime today) hours. In my image, at the time I tested it gave a correct "16".