The heavy covers and metal bindings of this compilation will not distinguish it from any of scores of semi-valuable, non-magical texts. 

This work contains certain secret formulae and prescriptions for unguents and exercises which enable a single reader to assimilate the text (3 days of uninterrupted study) and then practice the skills detailed therein. 

If this practice is faithfully done for 1 month, the character will gain 1 point of Dexterity. While the manual' will disappear immediately after reading, the contents will be remembered for 3 months (although the reader will not be able to articulate or otherwise record the information he or she retains). Only after the month of training will the Dexterity bonus be gained. 

Further perusal of a similar text will not add further to the same character's Dexterity.

Special Note. All magical books, librams, manuals, tomes, etc. appear to be "normal" works of arcane lore. Each is completely indistinguishable from the other by visual examination of the outer parts or by detection for magic aura. 

Bard characters will have normal chances of finding out the nature of such writings, as will an identify spell from a magic-user. 

Otherwise, only a wish will be useful in typing a magical writing, i.e. alter reality, commune, contact higher planes, limited wish, true seeing, true sight, and other spells or powers are useless. 

A wish will reveal general contents of a book, telling what characteristics or class is most affected (not necessarily benefited) by the work. It requires a second wish to determine exact contents. 

After being perused by a character, most of these magical works will vanish forever, but those which are non-beneficial to the reader will typically be attached to the character, and he or she will be unable to be rid of it. 

If the work benefits another alignment of character, the possessor is geased to conceal and guard the writing. 

As Dungeon Master you should use your judgment and imagination as to exactly how these items will be treated, using the rules herein as parameters.