You are looking for a small plastic screw-topped container, wrapped in camouflage tape and containing a logbook and room for a few small trackables or swaps.
Using the periodic table, you need to find values for the following elements:
Boron (A)
Oxygen (B)
Carbon (C)
Lithium (D)
Nitrogen (E)
Germanium (F)
(Again, the significance of these will be obvious at the published coordinates, although that probably won't help with the puzzle.)
Now for the formula:
N51 degrees, (E-C) (F/B) . (B-C) C (A*E-F) minutes;
W000 degrees, (C-D) E . (E-A) B (F-A-B-D-E) minutes.
(PLEASE NOTE that the above formulas were changed slightly on Saturday 10 December 2016 to accommodate a re-hide of the cache and subsequent error correction (oops! - thanks, Lydford Locators), so if you solved the puzzle before then, you'll have to re-solve to find the new location.)
All approaches to GZ may get muddy at times, and as the woodland floor does not get much direct sunlight, and rainwater may hang around. Suitable footwear is therefore strongly advised and I don't think any approach is suitable for buggies, certainly if it is muddy. There are nettles at GZ, but at the time of placement, there was no need to actually go wading into them.
There are a few other caches also in this lovely woodland, and the Hog's Back series is nearby if you're feeling up to a longer walk.
A quick note on the recommended parking: Although it may seem a little distance away, this is because parking on the Research Park is not allowed, and vehicles left there may get removed. Alternative pay and display parking is available at the nearby hospital, but you should avoid visiting times! Off-peak visitors may well find some parking spots on residential roads, but do check the restrictions.
Congratulations to BigMal70, Goldey36 & Drewpig for the FTF.