Doubt about gc's pause

[Enrico Colombini <erix@...>]

From the manual:
[[The garbage-collector pause controls how long the collector waits 
before starting a new cycle. Larger values make the collector less 
aggressive. Values smaller than 100 mean the collector will not wait to 
start a new cycle. A value of 200 means that the collector waits for the 
total memory in use to double before starting a new cycle.]]

What I miss is: what is the reference value?
I thought this could work:

  lua_gc(L, LUA_GCCOLLECT, 0);
  lua_gc(L, LUA_GCSETPAUSE, 120);

but I seem to be able to allocate memory way beyond 120% of the memory 
allocated before the collection, without starting an automatic gc cycle.
Looks like I don't understand how 'pause' works. I'm using Lua 5.1.2.

  Enrico