it's a bit pricey, I just use an ordinary cheap propelling pencil, but you need to have somewhere to put it where it won't get bent/snap.
I'm just started using a US graphite composite pencil which I like. Chisel end but bends a bit, think you can sharpen it on a brick like you do a stanley blade but haven't need to yet..
"chattahoochee carpenters pencil" on You tube but cannot find a uk supplier now, might have gone bust in the US