I also usually wear a cheap watch, so I can time the punt, helps me keep pace, know how long I got left, some hookers do take the piss and short change punters, a example of this, a few years ago in the Düsseldorf BahnDam a Moroccan girl did this to me, after a few minutes she said time was up, she wanted me to pay more, I got up, picked up my phone, that I'd set the stop watch, it showed only 6 minutes of a 15 minute punt, she let me continue, realised I wasn't a mug.