Time in sigil

So something like metric time, then?

Well, there are definitely more lawful (Lady's, Clerk's) and more chaotic (HiVe) sections of the city. Just assigning a base 10 system of keeping time wouldn't really change the city on a whole, as teH hIve is chaotic enough to balance it out.

Remember, "Time is an illusion, lunchtime doubly so."

Well, I chose 13 because it wasn't too metric a number (aka not 10), not based on our own time system (multiples of 6) and not too big or too small to cause a major change in daylength. I didn't think that much about symmetry.

However, it does seem important enough to be able to divide the day into at least two equal parts (day and night), and preferably that without breaking the hour. 16 hours seems logical, especially, as you pointed out, since there are that many outer planes. However, a 43+ earth-hour day is a bit much. I would suggest 8, as that would make a 22 earth-hour day, but it would make more sense (in my mind, at least) to have Sigil have slightly longer days. Thus, 12 hours a day (roughly 32 earth-hours per day) seems the best bet.

Sigil has seasons.

Um. It's Not the imperial system. It's a base 60 - it's what we *currently* use for degrees and radians. It is rather mathematically tight.

The Lady of Pain has an alignment? Let me guess, you got that from some WotC source. I wouldn't be surprised if they gave her stats next. It's all screed, she has no more alignment than does the Far Realm.

What I meant by bringing alignment into the conversation in the first place was that Sigil, not being a Lawful place like Mechanus, would be unlikely to follow a superlogical metric base-ten time system. Thus the natural day, that is the time between one peak and the next, would not have a round number of hours in it, unless those hours were designated in such a way as to fit evently (but then the hours themselves would not be round). The only way that Guvners could make everything perfect is by changing the length of the accepted second and working up from there, and while I would not be surprised at such from them, it would be far too confusing for a regular game.

If you mean twenty of those 2.78 earth-hour long hours in a complete cycle, then that would be a long day indeed.

The base-60 system for hours and minutes derives from the Babylonians. They used a base-60 system in dividing the circle into 360 degrees (6 equilateral triangles can be inscribed in a circle, each subtending 60 degrees of arc). This was intended for calendrical purposes, dividing the year into 360 days. It was for similar reasons that the Mayans used a numbering system which was base 20 in the units digit, base 18 in the second digit (for a product of 18*20 = 360), then base 20 in larger digits.

Calendrical calculations were by far the most important in the early development of mathematics, with the geometry and trigonometry being used for agricultural and religious purposes. Base-10 mathematics, used by the Egyptians with less mathematical sophistication, did not catch on as much in the early years and so base-60 calculations for degrees in a circle and associated timekeeping measurements became the standard.

The upshot of this for Sigilian timekeeping is that, without the backhistory, hours and minutes probably will be different. Note that the Guvners are now involved in post-FW days with keeping the "Hands of Time," a place in Sigil not much described. Since different planes on the Prime and the Great Ring may have wildly different calendars and even day lengths and year lengths, not to mention rates of time flow (and varying rates of time flow), a very useful service for people with cross-planar commitments would be a corporation dedicated to keeping track of astrological information, time and date on the various planes. Clockwork in pre-modern Sigil has not advanced to the point where small portable watches can be created, but with a large, fairly accurate timepiece and experts knowledgeable about planar and prime astronomy and calendar math would be able to provide various services. They could discuss relative planar time flow rates, calculate (or, in the case of chaotic planes, estimate) local times for such things as due bills or expiration of contracts, and send magical messages at preappointed times, generally serving as calendar translators.

Now, the Guvners being from Mechanus a base-17 system might appeal to them (the Great Modron March occurs every 17 major turns of Regulus, each of which takes 17 years), but the problem with a prime base for timekeeping is that it is in no way conveniently divisible. Let's instead examine how timekeeping might have naturally developed in Sigil.

You have peak and antipeak. People can tell when the light is roughly halfway between the two, and set their morning and evening by it. So we have 'half past antipeak' (morning) and 'half past peak' (evening). The first thing that seems convenient is to further divide the day into midmorning and midafternoon, giving us 'quarter til peak' and 'quarter past peak', and likewise the night around antipeak. This gives us 8 divisions of the day. If for convenience we divide each of these into a more easily digestible bite, we get 'one-eigth past peak,' 'quarter past peak,' 'three eighths past peak,' 'half past peak,' 'three eighths 'til antipeak,' 'quarter to antipeak,' 'eighth to antipeak,' and 'antipeak,' and likewise around the morning to peak. The day now has 16 divisions.

In the spirit of Cager slang, we might call these eighths bits (as in eight bits to a dollar, from some Prime world), or, if the Guvners are in the habit of ringing a good loud bell to mark the time, we could call them bells. So. We have a nice binary system of 16 hours a day, 8 between each peak and antipeak, called bells. And it wouldn't be long before some wag would be calling the crack of dawn 'the Mechanus bell,' the bell that signifies work is getting seriously started 'the Arcadia bell,' the peak bell 'the Elysium bell,' and so on around the Great Ring.

Within these you have minutes and seconds, but to anyone before the advent of precise clockwork that knowledge has almost zero utility. Second- and minute-timescale intervals are more likely to be measured in 'calm breaths' or 'as long as it takes to walk a mile' or something like that. For must-have research measurements, it might be in the binary spirit of this whole system to give 64 minutes per bell and 64 seconds per minute, leading to a second just slightly longer than Earth's.

Assuming that antipeak to antipeak is as long as an Earth day (or an Oerth day? Anyway...), a bell would be an hour and a half long in our units.

At 64 minutes per bell and 64 seconds per minute, Sigil's minutes and seconds would also be about half again as long as ours. (45/32 and 675/512 respectively, to be exact, but if you've a pressing need to convert between real-life seconds and Sigil seconds I want to use whatever portal you've got in your window.... ;^) )

At least one take on the Cager year already exists:

http://www.deathstar.org/~krlipka/ps/things/thoughts/sigilcal.html

Edit: Bah, Rip linked it first.

I mentally think of Sigil's calendar as "Sigil Reckoning," in the same sense that we use A.D. (Anno Domini), BC, BCE, and so on. "Sigil Reckoning" would probably be a de facto standard of timekeeping across the planes, even if some local areas use totally different systems for their own use.