makes sense, i was a little worried when i saw a pencil in the booth but this makes me feel better.

The UK election commission recommends pencils as there was a worry that ink could become invisible in the ballot box if there was an organised effort to replace the pens. But that’s the provided writing implement. I don’t think there is any rule for bringing your own. And I don’t think the counters have time to invalidate a vote because of marking type.