GE Monogram ZDP48N4G Owner's Manual page 16

All burners on the cooktop have two separate
Dual-flame
flames: a simmer (lower) flame and a main
burners
(upper) flame.
Simmering: Use simmer (SIM) to melt
chocolate, hold delicate sauces or for other
foods requiring low simmer heat.
Primary Cooking: Settings from LO to X-HI
will use both the main and simmer flames.
Use LO to HI for all purpose cooking. Use HI
or X-HI (highest setting) with 10" or larger
diameter cookware.
16
Surface Cooking
Stainless Steel Range
Simmering
Primary Cooking
Simmer Flame
Main Flame
Simmer Flame