Our very first investment agreement (3i as main investor with a local VC doing the legwork) had a table of equations defining various things that would effect how much founders and option holders would get in the event of an exit. Working out what these actually meant was non-trivial and we argued strongly against them - no luck.

Ironically when we went public we made a chunk of money from the very ratchet agreements we had argued so vigorously against (combined with help from the taxman).