Software engineers without true random number generators often try to develop them by measuring physical events available to the software. An example is measuring the time between user keystrokes, and then taking the least significant bit (or two or three) of the count as a random digit. A similar approach measures task-scheduling, network hits, disk-head seek times and other internal events. One Microsoft design includes a very long list of such internal values, a form of cryptographically secure pseudorandom number generator. Lava lamps have also been used as the physical devices to be monitored, as in the Lavarand system.