Just got my Ultragauge, so...
There is another option. There is a "smart" fuel level setting that will detect a fillup and automatically reset the DTE calculation (it basically "arms" when you hit a certain level of the tank, and then resets when armed and above another level in the tank - both of these levels are user settable, with the defaults being something like 50% and 98%. Mine didn't work the first time, but I have to make sure it's turned on and verify where it think my tank is.
In "smart" mode it also calculates fuel used based off the injectors (I think) and your fuel tank size (set by the user) instead of using the fuel tank sending unit, which tends to be off (showing 100% for the first 60 miles on my car, and 0% with 80 miles before the engine stutters)
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