From the longer Wikipedia page 
In Lebor Ogaim ("The Book of Ogams"), also known as the Ogam Tract, is an Old Irish treatise on the ogham alphabet (Wikipedia page ). It is preserved in R.I.A. MS 23 P 12 308–314 (AD 1390), T.C.D. H.3.18, 26.1–35.28 (AD 1511) and National Library of Ireland MS G53 1–22 (17th century), and fragments in British Library Add. 4783. It does not bear a title in the manuscripts, but it is mentioned in the Auraicept na n-Éces (2813f.) as amal isber in leapar ogaim, whence the commonly used title. The Ogham Tract is independent of the Auraicept, and is our main source for the Bríatharogaim.
The Ogam Tract also gives a variety of some 100 "scales" of variant or secret modes of writing ogham (92 in the Book of Ballymote), for example the "shield ogham" (ogam airenach, nr. 73). Even the Younger Futhark are introduced as "Viking ogham" (nrs. 91, 92). Some of these are word lists based on the alphabet, and some seem to involve a numerical system of tallying. Most however, are simply variations on ways of writing the alphabet. They are examined for their significance by Macalister (1937) and by McManus (§7.11, 1991).
The training of the Gaelic poet or file involved learning one hundred and fifty varieties of ogham – fifty in each of the first three years of study, and it is clear that most of these are the varieties given in The Ogam Tract (McManus § 7.13, 1991). Macalister sees them as evidence of ogham's cryptic nature, and as serious examples of how the alphabet was used for secret communication. According to McManus, however, the practical benefits of the alphabets are not so clear. The word lists at least may have provided access to an extensive vocabulary classified in a convenient manner, but these are only a small number of the total, and he regards the rest as nothing more than the result of the fascination of the Medieval mind with cryptic alphabets. However, some of the varieties indicate a possible use as property or business records and tallies, and it may be that the many cryptic varieties were deemed worthy of study in themselves as a means of training the mind in the use of words and concepts.