Roll-under in Classic Traveller
Using my best Kirk Douglas voice, let me say "I'M Jonathan Sherlock!".
Thanks to all commentators here. You all now know what I look like. I have now been accused of "bias" in the comment thread under my blog post, and I will be addressing that at some point.
I do agree with others that there are problems with T5, but I am really excited (if it wasn't obvious already) about this core rule book. Marc Miller has made careful, balanced choices to stitch a universe together without becoming totally bogged down.
Now, admittedly, the Roll-under tradition is not in the core 3 LBB's (at least, not that I could see). But within the broad Traveller Canon dating back to the original game, this mechanic existed. It was certainly not the dominant mechanic, but it did exist quite prominently. Effectively we had a variety of mechanics to do with dice, and starting with Mega Traveller these were unified in UTPs at which point roll-under characteristic checks were subsumed into tasks that did not have a skill, e.g. To push the boulder off the edge of the cliff: Difficult, Strength, 1 combat round (absolute).
In published adventures there were a few variations of "check a characteristic" by rolling 2 dice and comparing the result to the relevant score.
Many examples can be found, but check in particular
page 28 of The Traveller Adventure where this mechanic is spelled out under the heading "The Uses of Dice Rolls".
For the record, I refereed The Traveller Adventure for a group of players at my high school in the mid 1980's.
It was loads of fun and we had a few side adventures along the way drawn from JTAS Amber Zones. Best Traveller campaign I ever ran.