Geoscience Geocache Multi-Cache
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Size: 
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A single off-set multi-cache.
Geoscience Australia is responsible for conducting much research in the Geosciences. I couldn’t possibly describe all their functions here, so if you are interested, it would be best to visit their website at: http://www.ga.gov.au.
Part of what GA does is to produce maps! Now, I’m sure that all you dedicated geocachers have used maps! (Well, at least those of you that have ventured beyond the suburbs to find caches).
Now, to use maps, you need to be able to determine where you are accurately! This is done by referencing your location against a know location. Over the years the method of determining where you are has changed. These methods are defined as Datums. GA have been responsible for providing the datums used in Australia. See http://www.ga.gov.au/geodesy/datums/history.jsp for a history of Australian datums.
Suffice to say, without datums, Geocaching would not be possible! Geocaching uses the WGS-84 datum. This is an American datum, but luckily, it is similar to the current Australian datum (GDA94).
If you have ever used a map, you will notice that it states the datum used on the map. Many older maps use the AUSGEOD-66 datum. If you want your GPSr to match your map, you need to change the datum to that of the map, otherwise you might be around 200m out!
What is the difference between GDA94 and WGS84?
In January 1994, GDA94 and the International Terrestrial Reference Frame (ITRF) coincided. At around the same time, the WGS84 reference frame was also aligned with ITRF. For most practical applications where an accuracy of about a metre is required, GDA94 coordinates can be considered the same as WGS84.
Anyways, on to the cache...
The listed coordinates will take you to GA. Please note, you will need to enter the building to obtain most of the required information. Therefore, you will only be able to get that during business hours.
Once there, you need to find the following information:
A = The hour represented on the clock in the Eschenhagen Magnetograph - 1.
B = number of core samples taken from the stalagmite -4.
C = Last digit of the year this building was opened -6.
D = The upper estimate of the age of the stalagmite (in millions of years) + 1.
The cache can be found at 35 20.AB5, 149 09.CD2.
Now - just to make sure you have been paying attention – the final coordinates are in the AUSGEOD-66 datum! (Not WGS-84)
Please BYO pen.
Additional Hints
(Decrypt)
srapryvar