Question about Clock Trigger for Solo-synth Envelopes

[AlenK]

There is a parameter, Clk.Trg, that allows an envelope in the solo synth to be synchronized to the beats of the MIDI clock. Actually, the description in the manual says it "specifies the number of beats for resetting the envelope." There are settings Off, 1/4, 1/3, 1/2, 2/3, 1, 3/2, 2, 3 and 4. These seem to to act like different timing quantizations.

 

There are also settings for the same divisions of the beat but with a "U" appended on the name, about which the manual says "Selecting a setting from 1/4U to 4U resets to the timing of the back beat." Can someone explain to me what that actually means in terms of timing?