Quote:
A book on a rare script used in astrological/numerological manuscripts of the Lanna people.

The primary use (which is not completely explained) lies in astrology and numerology.
The structure of the encoding is primarily numerologic (using "hora' [astrology] numbers), with some modifications, where Tham (Buddhist) letters are numerologically identified and correlated.

The initial thoughts are that this is an example of indigenous astrology/horoscope/numerology, where a tantalizing clue can be found on page 41 of the scans -- the middle set of text is in old Tai Neua/Ahom (whose astrology/numerology have been well documented). Since in the Lanna/Laanxaang regions, were primarily religious in nature, Yuttasara may have been the mechanism by which to circumvent potential religious strictures by being secular in nature, but not administrative (where would have been used in Lanna/Laanxaang contexts; Khuen regions most likely used Burmic or Shan instead). I have purposely omitted mention of the Lue in Sipsongpanna in the above conjecture, because the Lue in Sipsongpanna have extended the use of to write their astrological treatises, as well as medicinal treatises.

The examples with the small circles below are reminiscent of Semitic/Greek numerology, where each letter has a numeric value for other calculations.

Tai-Kadai