Editing D'ni time conversion (section)

== Calendar Conversion Factors ==

The equivalence factors for surface time given in the tables above are, unfortunately, far too imprecise to be useful for converting between the Cavernian and Gregorian calendars. Also, were are missing one other piece of vital information: a starting point. Just as we need to know that 0° Celsius is exactly equal to 32° Fahrenheit before we can convert temperatures between the two scales, we need to know of at least one date in the Gregorian calendar that is exactly equivalent to one particular Cavernian date, before we can convert between the calendars. Until recently, such a "rosetta date" has never been directly provided and the required factors had to be derived from indirect evidence.

In 1997, [[RAWA]], [[Cyan]]'s D'ni Historian, provided a list of surface dates corresponding to the start of the D'ni New Year (Leefo 1) in several years<ref>https://web.archive.org/web/20120310223201/http://www.fortunecity.com/underworld/riven/473/dninewy.html</ref>. This list is is reproduced below.

{|class=wikitable
! colspan=2 | Official Dates for Leefo 1 (PDT)
|-
| 1998 || 4/21 2:35:17 AM
|-
| 1999 || 4/21 8:24:03 AM
|-
| 2000 || 4/20 2:12:48 PM
|-
| 2001 || 4/20 8:01:33 PM
|-
| 2002 || 4/21 1:50:18 AM
|-
| 2003 || 4/21 7:39:03 AM
|}

''The times shown above are in Pacific Daylight Time, which is UTC-0700.''

While the above list does not provide us with the equivalent D'ni ''hahr'' for each year, it does give us a figure for the length of the ''hahr'': 31556925 seconds, or 365.2421875 days. This makes the D'ni ''hahr'' about the same length as our astronomical mean solar tropical year, which is why the Cavernian calendar includes no corrections equivalent to our leap years.

The time given for 1998 was originally believed by the author to be a transcription error, because it is one second off from the intervals shown in the rest of the list, so it was ignored in the above calculation. However, in light of new information, the deviation appears to be the result of a slight rounding error.

The actual conversion factor for the ''hahr'' was revealed by RAWA in October 2007 to be 31556925.216 seconds, or 365.24219 days, which was the length of the mean solar tropical year in 1995. Thus, the correct table of key factors is:

: 1 Hahr = 365.24219 days = 290 yahrtee
: 1 Yahr = (365.24219 / 290) = 1.25945582758621 days
: 1 Day = (1 / 1.25945582758621) = 0.793993705929756 yahrtee

If desired, precise conversion factors between other surface and D'ni time measures can be derived from the above, but these are all that are needed for the purpose of performing calendar conversions.

[[File:CyanCam Dni new year cake.jpg|left|frame]]The evidence originally used to determine the correct Cavernian ''hahrtee'' matching the date in the table is more indirect. In April of 1997, Cyan revealed the Riven Journals Web site (now defunct) as a teaser site for the upcoming release of ''Riven: The Sequel to Myst''. The opening of the site was first announced by Jim Stephenson, editor of the Unofficial Riven Homepage (also defunct) on April 22, two days after the beginning of the D'ni New Year in 1997. At about this time a Web cam in Cyan headquarters (Cyan Cam) showed an image of a cake that Cyan prepared to celebrate the event. Written on the cake in D'ni numerals was the base-25 number [15|11|3] (<dni>%!3</dni>), which is 9653 in base 10. Presumably, this was the number of the ''hahr'' that began on that D'ni New Year in 1997 CE.

Based on this reasoning and the assumed one-second error in the 1998 time value, the "rosetta date" for Cavernian/Gregorian calendar conversions was determined to be:

: '''00:00:00:00, Leefo 1, 9654 DE = 9:35:18 UTC, April 21, 1998 CE'''

However the correct date of calendar convergence was disclosed in October 2007 to be the date/time stamp of the HyperCard Stack for the original MYST game: April 21, 1991 at 9:54 AM PS(D)T. Thus:

: '''00:00:00:00, Leefo 1, 9647 DE = 16:54:00 UTC, April 21, 1991 CE'''

''Note that the surface time has been corrected from Pacific Standard (actually Daylight) Time, as supplied by RAWA, to Coordinated Universal Time (UTC, aka GMT). For purity's sake, it might be more appropriate to use Mountain Daylight Time (UTC-0600), which applies to the state of New Mexico under which the D'ni cavern lies. However, the use of UTC makes it easier for individuals to apply their own local time-zone corrections.''

With conversion factors and convergence date in hand, we can proceed to a description of the specific calculations involved.