Talk:Navigation and Longitude
If there was a way of knowing the local Alusian time on board ship then longitudes are not too difficult to calculate using an ephrimus and a sextant i.e. if your reference star is crossing the meridian at Alusia at time x ... and determining how high the reference star is where the ship is.
I suppose one way of having a reasonably accurate clock is to know the Alusian time when a small mammal is killed as the ship sets sail, then keep asking the DA question 'Time since death' on the corpse.
--Keith 20:38, 28 Dec 2007 (NZDT)
This is true. However, the "fish clock" use of DA is accurate but not precise. An answer of "several hours" isn't going to be enough to get much accuracy in determining your position, and as the weeks goes by, "several weeks" is going to be even less useful. Also, sextants aren't available except to the Destinians (and special off-world items?), and cross-staffs just don't have the accuracy - epheremedes have been calculated, but the measurement error on a ship is still just too high - hence the recommendation for Mariners to just keep an accurate log.
Instant communication with a fixed base thousands of miles away (range-less mind speech or crystal of vision), or a magical timepiece, or any one of many magical devices might give precise answers as to the time in another location, which would be enough to determine Longitude, but that's outside the scope of this work.
--Andreww 01:39, 29 Dec 2007 (NZDT)