The R:2R ladder shown uses resistors of only two different values with a ratio of 2:1. An N-bit DAC requires 2N resistors. There are two ways in which the R:2R ladder network may be used as a DAC, known respectively as the voltage mode and the current mode (they are sometimes called "normal" mode and "inverted" mode, but as there is no consensus on whether voltage mode or current mode is the "normal" mode for a ladder network, this nomenclature can be misleading). Each has its advantages and disadvantages.