60' is cake (well, not 'cake', but certainly nothing I'd sweat taking a non-certified friend down to if it was clear and calm and they weren't an idiot)...it's at 120' when you start feeling woozy that things get interesting.
My girlfriend has a floor of 80'...below that and she starts freaking out just because she knows she's deeper than 80' (arbitrary I know...but what can I say, I'm not in her head). I've been thinking it'd be great to get a depth gauge that just snags at 80'

she'd be good for anything.