"I'm a leaf on the wind...

According to Wookieepedia, there’s a Galactic Standard Calendar and a Galactic Standard time based on Coruscant’s orbit. From here: 

• 60 seconds = 1 minute
  
• 60 minutes = 1 hour
  
• 24 hours = 1 day
  
• 5 days = 1 week
  
• 7 weeks = 1 month
  
• 368 days = 1 year
  
• 10 months + 3 festival weeks + 3 holidays = 1 year
  
• 10 years = 1 decade
• 100 year or 10 decades = century

Apparently, there were 20 different calendars in use during the Old Republic, with a 10-month standard calendar variant being used by the Republic Judiciary right before the Clone Wars (which I guess is where these numbers came from?). There was also an 11-month variant used by archivists and a hexadecimal-based on used by infrastructure. But even if the number of months in a year differ (and therefore introducing variation in the rest of the time measurements), I’d guess that the seconds, minutes, hours, and days would be the same. Oh, the number of days in a week might vary from calendar to calendar, too, I suppose.

Days of the weeks are:

• Primeday
  
• Centaxday
  
• Taungsday
  
• Zhellday
  
• Benduday

The festival weeks, for anyone who’s curious are: New Year Fete Week (took place before the first month), Festival of Life (between months 6 and 7; included parties and gift-giving), and Festival of Stars (between months 9 and 10, celebrated interstellar space travel; many took vacations to other planets to celebrate).

Anyway, so I would guess that while each planet probably had its own calendar and time measurement system, for interplanetary trade and travel purposes, the Galactic Standard Calendar would be used.

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So what I’ve done, personally, when writing in PT time (because I definitely can’t use BBY, they don’t even know that the battle of Yavin is gonna happen one day) is to use certain notable epochs, that they might use to restart the numbering system of years.

There’s the Ruusan Reformation (1000 BBY) and the Great ReSynchronization (35 BBY). The Ruusan Reformation, once enacted, resulted in the Republic Measures and Standards Bureau resetting the year zero to the year of the Seventh Battle of Ruusan (which is 1000 BBY per the Galactic Standard Calendar).

The Great ReSynchronization was established in 35 BBY by the Republic Measures and Standards Bureau to recalibrate the dating systems (it was disbanded in 25 ABY during the New Republic, so it only lasted 60 years; but I’m guessing that for people living during those years (including the Imperial Empire), they probably went with the new numbering system). So, the Battle of Geonosis took place in year 13, for example. Dates were written [Year]:[Month]:[Day]. Dates before ReSynchronization were written with BrS (before resynchronization; there were no trailing characters after the date for post-resynchronization).

If you look up certain years on Wookieepedia, they’ll tell you the equivalent in these other dating systems. So for example, 32 BBY (the Battle of Naboo) is year 36,421 after the Tho Yor Arrival, year 3,621 after the Treaty of Coruscant, year 968 after the Ruusan Reformation, and year 3:3-4:2 after the Great ReSynchronization. The Wookieepedia page for those years will also list all the events that happened in that year. It’s a great reference.

A summary from my latest venture onto Wookieepedia, because I’ve been watching some of the clone-centric CW episodes with @themikeymonster and had Questions about the clones. 

Italicized information is from Legends, regular font is from canon. 

More musing and headcanons under the cut. Please feel free to chime in. This is making my head hurt.

Null-class Advanced Recon Commandos

• Prototypes
  
• Designation: N- or Null-
  
• Total produced: 12 (but 6 died early on)
  
• Deemed a failure by Kaminoans; adopted by Mandalorian mercenary Kal Skirata
  
• Named after Mandalorian warriors
  

Alpha-class Advanced Recon Commando (ARC) troopers

• Designation: A- or Alpha-
  
• Unaltered independent minds - only some of them decided to obey Order 66, the rest sided with the Jedi
• Total number produced: 100
  
• Personally trained by Jango Fett, who ordered them to kill all the younger clones if Kamino ever fell to the Separatists
  
• Known trooper:
  • Alpha-17

Clone trooper commanders

• Designation: CC-
• Bred for leadership roles, with extra capacity for autonomy, tactical thinking, and coordination
• Trained with ARC skills
• Led regiments of 2,304 troopers
  
• Some known troopers:
  • CC-2224 - Cody
  • CC-3636 - Wolffe
  • CC-5052 - Bly

Clone Commandos or Republic Commandos

• Designation: RC-
  
• Bred with more independence than standard clone troopers
• Trained to be more lethal and efficient than average clone soldier by Mandalorian drill sergeants
• Worked in squads of 4, carried out covert infiltration, sabotage, demolition, and assassination
• A few refused to comply with Order 66
• Known troopers:
  
  • CC-5576-39 - Gregor
  • Foxtrot Group - attached to the 212th; led by Gregor
  • Clone Force 99 - genetically altered to be super soldiers; worked with Cody; named in honor of 99
  • RC-1138 - Boss; leader of Delta Squad

Clone trooper captain

• Commanded companies of 144 troopers
  
• Bred as battlefield officers and special mission operatives
  
• Known troopers:
  
  • CT-7567 - Rex

Clone Lieutenant

• Designation: CL-
  
• Commanded platoons of 36 troopers
  
• Known troopers:
  
  • CL-9632 - Trap

Clone Sergeant

• Designation: CT-
• Commanded squads of 9 troopers
  
• Known troopers:
  
  • Appo - later promoted to clone commander

Rank-and-file clone troopers

• Designation: CT-
  

From what I’ve been able to gather, rank-and-file clone troopers can also be promoted to higher classes, which probably explains all the variations in the clone number designations. Some clones were meant to serve in those higher level positions so were given the appropriate designations at birth and others worked their way up, and kept their CT- designations in their new roles. Also, ARC trooper training could be offered to any of the clones, such as Fives (CT-27-5555) and Echo (CT-21-0408)

The variations of numbering within a squad, I have no idea about. For example, Domino Squad were clearly being raised and trained together, right??? Should they not have all been from the same batch? But the designations are CT-782 (Hevy), CT-00-2010 (Droidbait), CT-21-0408 (Echo), CT-4040 (Cutup) and CT-27-5555 (Fives). Why do some of them have the extra 2 digits in front of the last 4 but others don’t? Why does Hevy only have a 3 digit designation? By the time of their training, the cloning process has been going on long enough that I would have expected the Kaminoans to have figured out a numbering system that made sense.

So I decided to sit down and try to make sense of the GAR and its many divisions…..many days ago. It has been a massive undertaking, lol. But here’s what I’ve got, for anyone else who’s also interested in using this for worldbuilding.

Shoutout to @themikeymonster for listening (so to speak) while I went through my thought process for this.

This is the basic structure of the GAR:

This is what Wookieepedia says about the Sector Armies:

• The 2nd was led by Mace
  
• The 3rd army often reinforced the 12th and was the reserve unit for the Mid Rim
  
• The 4th army is led by Mundi and reinforced the 13th; was known as the Outer Rim Sector Army later
  
• Most of the 5th army was transferred to more active battlefields, since that covers the Deep Core; only a skeleton force remained there
  
• The 6th had repair yards and training camps
  
• The 7th supported the 5th and conducted secret scouting missions beyond the frontier
  
• The 8th saw lots of intense fighting and was reinforced by many of the reserves
  
• The 12th was charged with invading some of the Separatist strongholds in its area
  
• The 13th defended Kamino; it included the Hutt territory but there weren’t a lot of forces deployed to those areas; it was reinforced by the 4th and 14th
  
• The 15th was a reserve force primarily
  
• The 16th was mostly defensive and was meant to be able to move Coreward if necessary
  
• The 17th reinforced the 18th
  
• The 18th was under the command of Tarkin (who worked with Piell)