INL (Integral Nonlinearity) is a measure of the linearity of an ADC or DAC. It describes how the data converter transfer function varies from an ideal straight line. A maximum INL of ±1 LSB or better means this variation is within the resolution of the data converter, and DNL better than -1 LSB guarantees monotonicity. In a monotonic DAC, the analog output always increases or remains constant with increasing input code. Non-monotonic behavior means that for an increasing DAC input code, the output amplitude may decrease. In closed-loop systems, non-monotonicity can change negative feedback into positive feedback. High linearity is desirable for open loop systems, and in applications where a widely varying parameter (like speed) needs to be continuously controlled. For a system with excellent INL, it is only necessary to correct for offset and gain errors which is easy to do, while for a system with poor INL it may be necessary to correct the entire transfer function which is more difficult.