I just remembered when I learned it. We were on holiday and my parents and brothers went for a walk in the mountains and I stayed behind in the motor-caravan. By the time they got back, I had got something in C like play bass notes G,A,B to lead to the C bass, chord, then hammer on the D string to play an E bass with the C chord. Similar bass notes but to lead to F, couple of F chords, few bass notes to get to G....

At a guess, it must have taken me about 3 hours to learn how to do this and at a reasonable pace. Mindyou, I would have been about 15 then. I don't pick things up easily now and it took me years to find the next new thing.

Jon