Then, as I leveled off at 13,000, neither one of us could remember for sure what altitude we were actually assigned. John asked ATC to confirm our assigned altitude and was told it was Flight Level 230. He put the assigned altitude in the alerter, and I immediately climbed to it. This wasn't an altitude bust since we were cleared all the way up to Flight Level 230, and we lingered only briefly at 13,000. No harm, no foul, but still — it wasn't perfect.