AEG C81700K Installation And Operating Instructions Manual page 15

The middle ring is switched on. The control indicator under the
symbol II is illuminated.
4. Pressing the "booster" sensor field again activates the outer heating
ring. The control indicator under symbol III is illuminated.
5. To switch off the outer heating ring touch the "booster" sensor field;
the corresponding heating ring is switched off.
Operating Instructions
109