Metal Film Resistors are made by depositing a resistive element on a high-grade ceramic rod. The resistive element is the film may be carbon, nickel chromium or a mixture of metal & glass or metal & metal oxide. The precise resistance is achieved by removing part of the film in a spiral pattern around the rod. Tolerances of +/-1% can be acheived with metal film resistors. This means that a 100 ohm 1% resistor would in the range from 99 to 101 ohms.