BRIDOL is the British Sundial Society's Register of Fixed and Mass Dials, which gives detail and photographs of about 8000 fixed sundials and 3000 mass dials in the UK.
Some of these are in private gardens, but the majority are publicly available.
The dial is in the form of a helix around a long polar gnomon held in a crescent shaped frame. The helix can rotate around the gnomon to adjust for the equation of time, which is indicated by two concentric rings of months, one offset so that by aligning the date the right correction is applied.
Ref: See BSS Bulletin 15(iv) pp144-145.
