Trimming bottom of cornice - best tools / techniques?

[shump]

I need to trim 10mm from the bottom of a cornice to fit in a wall mounted airconditioner. The unit is about 1m long. What would be the best way to do this? Not sure I'm happy to attack it with a chisel!

[Pulse]

Shump, just check the clearances that are required around the machine, you could probably use a stanley knife with a metal ruler if needed

Cheers
Pulse

[Bluegum]

As pulse has said. I would go the stanley knife and stell rule option as well.