There are two rocker switches. The wide one, white plastic, is the normal/gentle button. Normal gives almost continuous tumbling in wash with only a brief pause before reversing. Gentle gives three short bursts of tumble in each direction with pauses in between, before reversing. (ie: clockwise-pause-clockwise-pause-clockwise-pause-clunk(timer increments)-anticlockwise-pause-anticlockwise-pause-anticlockwise-pause-etc.) I think gentle gives a short spin, too.
The illuminated button (smaller, orange plastic) is the spin/hold button. Lights up orange when hold is on.
The timer is another giveaway that it is a slow spin machine. The older machines have the dial which covers all the way around for one cycle. The later ones have a split dial, first half is normal cycle with 800 spin, second half is gentle cycle with 500 spin. Older models have the two rocker switches as above, with fill temp selected by the cycle - 1 and 2 are hot fill, 3 is warm fill, 4 is cold fill. No heater if model number ends in 0, heater models end in 5. (470, 480, 490 have no heater, 475, 485, 495 have heater.)Heater models always heat to temp, you can't select a no heat cycle. No dispenser drawer. On/off by pulling timer in/out.
Newer models have dispenser drawer, select wash temp with push buttons hot/warm/cold, push buttons to select spin or hold, on off button, heater models have heater on/off button.
I can not be 100% certain that the 520 is slow spin as I have never been inside one, but all the evidence points that way. It would be very interesting if the 520 had the old model controls but the fast spin...
chris.