Thanks to David Evans for this picture. He writes:

I discovered this clock in Cpo SS Apostoli in Venice (between Ca D’Oro and Rialto Bridge. Can anyone explain how you use it?

The vagaries of medieval and renaissance Italian time-keeping are mentioned elsewhere on the site. My understanding is that the Italians started their counting from 1 at twilight or sunset, and counted all the way through the night, reaching 24 just before sunset (if things went like clockwork).

I don’t know whether ‘the authorities’ run any of their surviving clocks on the original schedules, maintaining the authentic ‘Italian hours’, for the benefit of tourists and the inconvenience of the residents. The central pointer is similar to the other Venice clock, although perhaps less easy to read. To my eyes, this clock says about 6. It’s obviously not midnight or 6 hours after sunset, so I think we can dismiss the ‘Italian hours’ idea. If the picture was taken at 6 or 7 in the morning (allowing for Daylight Saving Time), then the clock might either be working really well, or it’s broken, the photographer was lucky enough to be there at the one time of day when the clock was reading the right time.

More likely, though, the clock is either not working or not keeping the right time. You’ll have to go back and do some more research, David!