safety interlocks between the fuel source and the ventilation, as may be required with gas systems. Applications Induction equipment may be a built-in surface, part of a range, or a standalone surface unit. Built-in and rangetop units typically have multiple elements, the equivalent of multiple burners on a gas-fueled range. Stand-alone induction modules are typically single-or dual-element. All such elements share an electromagnet sealed beneath a heat-resisting glass-ceramic sheet. The pot is placed on the ceramic glass surface and heats its contents. Asian manufacturers have taken the lead in producing inexpensive single-induction-zone surfaces. In Japan, some models of rice cookers are powered by induction. Induction cookers are less frequently used in other parts of the world. Induction ranges may be applicable in commercial restaurant kitchens, with lower installation, ventilation and fire suppression equipment costs. Drawbacks for commercial use include possible breakages of the glass cook-top, higher initial cost and the requirement for magnetic cookware. Controls Some units have touch-sensitive controls. Some have a memory setting, one per element, to control the time that heat is applied. At least one manufacturer makes a "zoneless" induction cooking surface with multiple induction coils. This allows up to five pots to be used at once anywhere on the cooking surface, rather than in pre-defined spots. Cookware Cookware must be compatible with induction heating; generally, only ferrous metal can be heated. Cookware should have a flat bottom since the magnetic field strength (heating power) drops rapidly with distance from the surface. (Wok-shaped cooktops are available for use with round-bottom woks.) Induction disks are metal plates that are heated by induction and heat non-ferrous pots by thermal contact, but these are much less efficient than ferrous cooking vessels. Induction-compatible cookware can nearly always be used on other stoves. Some cookware or packaging is marked with symbols to indicate compatibility with induction, gas, or electric heat. Induction cooking surfaces work well with any pans with a high ferrous metal content at the base. Cast iron pans and any black metal or iron pans are compatible. Stainless steel pans are compatible if the base of the pan is a magnetic grade of stainless steel. If a magnet sticks well to the bottom of the pan, it is compatible. Non-ferrous cookware is compatible with "all-metal" cookers. Aluminum and copper are desirable in cookware, since they conduct heat better. Because of this, 'tri-ply' pans often have an induction-compatible skin of