pH controller sensitivity

I'm resetting up a planted tank, torn down due to a move.  While it is already
torn down I'm going to add a couple of odds and ends to it, including
automating my CO2 system, adding more light, and substrata heating.

For controlling CO2, temp, lights and fan, and so on I'll be using a data
aquisition card, an old PC, solid state relays, and I'll write the code in C or

Do have a question though for those of you with pH controllers.  How precisely
is the pH controlled by these?  I have seen some with +- 0.02 but am unsure
just how precisely I should control the pH of a tank.  Is 0.1 enough or should
I use finer settings?  I can control it up to the precision of the probe
itself, but just do not know if I need to or if I can use a wider range of

Appreciate any advice you may have.

Doug Valverde 75051.160 at compuserve_com (with no local node for the Net)