dimension arc length

Someone else brought this up in the 2004 group but didn't get an answer.  There used to be a way to dimension an arc length.  You could cycle between degrees and length by pressing space.  Why this was changed, I don't know.  There is a setting in the dimension style to have it do length or angle but that seems stupid as you would need to setup a dimension style for each.  I found a key-in command that does exactly what I'm looking for but I haven't been able to find the button to do it.  DIMENSION ARC SIZE

Anyone have an answer?