> Are they numbered from sunrise, with sunrise=0, one hour later as 1 > two hours since sunrise as 2 etc?
Yes, correct. > Italian hours. I understand these to be the hours until sunset. No, in their original use they are counted since sunset. > I would take these to also be 1/24 of a day in length. Is sunset=0 > and one hour before sunset=1, etc? Therefore sunset=24 and one hour before sunset=23. But of course you are free to number your sundial with 24-italian which is more useful nowadays. To make it a bit more complicated: In Italy and southern Switzerland some regions counted the hours half an hour after sunset so that sunset=23:30. > What exactly is a bifilair sundial? I take it that it has two planes A bifilar sundial has two shadow casters in form of straight lines not parallel and not intersecting. But the intersecting shadow lines give the time. Maybe Fer de Vries can give some more details. > Can we draw a sundial from these equations? How are a and b related to > latitude, declination of the sun, and hour angle? This will keep me off The hyperbola usually give the lines for a given declination of the sun. It is possible to deduce a and b from the walls orientation and the suns declination. - Daniel Roth, Arbeitskreis Sonnenuhren, Germany
