You can only use one or the other to do what you want to do.
If autolap is on, if you try using the lap/split button, it will then autolap everytime you go past those points again until you stop and reset the garmin.
If you want to do splits, you need to turn autolap off.
Autolap works fine for me on an outdoor (obviously) 333m track, but as Carleton mentioned, you really need a speed/cadence sensor for it to be accurate (which I have). I just start it at the start of the session as I am rolling over the finish line, and it will click over every time I complete a lap. On the odd occasion you will a half or double lap, but not much.
JMR
Thanks for all the replies, but I am still a bit confused.
if I get a speed/cadence sensor will it work accurately with auto-lap (by location)? I understand that I can't get splits - all laps will be recorded.
I presume satellite accuracy will vary between tracks depending on the number of satellites engaged etc?
Using the start/stop button isn't feasible for the short efforts, but I can also understand that the data isn't of much use if not accurate.