apenwarr/afterquery — pull request #1 by DentonGentry (2013-04-12 23:16:28+00:00)
Title: Delta operator for afterquery

Computes the difference between successive samples.
1. If the value increases, emit the difference.
2. If the value decreases, emit the value.
3. If the value does not change, outputs undefined

This is most useful for a heatgrid of a continuously
increasing counter, to show where the counter changes.