Homeopathy: Medicine for the 21st Century
There are three scales of homeopathic potencies, with succussion or agitation performed at each step of dilution:
Decimal (x) scale - dilutions are made at the rate of 1:10, so 3x = 1:1,000;
Centesimal (c) scale - dilutions are made at the rate of 1:100, so 2c = 1:10,000;
LM (or Q) scale - dilutions are made at the rate of 1:50,000, so LM2 = 1:2,500,000,000.
The decimal and centesimal potency scales perform similarly, and certain potencies have been found to be more generally effective than others. [1,2] The most commonly used potencies in the UK are 3x, 6x, 6c, 12c, 30c, 200c, 1m (1,000c) and 10m(10,000c), though higher potencies and potencies in between these ones are also used on occasions. These potencies are usually given in single doses at intervals which depend on the individual’s reaction, with the interval and the possible repetition of a particular potency depending on the nature of the symptoms, the potency and other factors.
On the other hand the LM scale has a very different pattern of prescription, since a prescribed LM potency is regularly repeated, being succussed and often then diluted by the patient before taking each dose. Prescriptions start with one potency (usually LM1) and then step up to the next (i.e. LM2, LM3, etc.) as needed. The reactions to centesimal (and decimal) and LM potencies are generally different. 
1. James Tyler Kent, New Remedies, Clinical Cases, Lesser Writings, Aphorisms and Precepts (New Delhi: B. Jain Publishers, repr. edn 2001), pp. 358-59.
2. Michel Schiff, The Memory of Water: Homoeopathy and the battle of ideas in the new science (London: Thorsens, 1994), pp. 25-28.
3. Robert Barker, LM Potencies: A selection of articles giving a practical guide to their use (Sheringham: The Homoeopathic Supply Company, 1997)
Why it works