Integers, the counting numbers, are a subset of discrete numbers. Even if a variable is continuum valued conceptually, in practice it might be discretized. An example is time in a digital simulator. Whether the time in a simulation is discretized into 0.1 s increments, millisecond increments, or whole-second increments, the simulated time can only have discrete values. Whenever some variable is placed in cells or array elements, the interval is discretized. Other examples include spatial increments in solving a differential equation (even though distance may be continuum valued) or bin increments in creating histograms.