You can measure a cycle beginning anywhere, but to begin with a tao or Rei glyph would seem to be the natural choice:

Ga1-22 (464)	Ga1-23	Ga1-24	Ga1-25
Ga1-26 (468)	Ga1-27	Ga1-28	Ga1-29	Ga1-30 (472)

Tao shows a canoe 'en face' while Rei is seen from the side. 26 * 18 = 468 suggests an 'antipodal' glyph could be at 13 * 18 = 234. Counting from Ga1-30 eliminates the first 29 glyphs and the last glyph on side a will therefore be number 200:

a1	(30) 1	b1	26
a2	29	b2	35
a3	24	b3	30
a4	27	b4	33
a5	30	b5	29
a6	29	b6	28
a7	34	b7	31
a8	26	b8	30
sum	(229) 200	sum	242

Gb2-8 (maybe Venus) at 13 * 18 = 234 could then be a sign that Sirius (Te Pou) is coming:

Gb2-8 (234)	Gb2-9	Gb2-10	Gb2-11	Gb2-12
Gb2-13	Gb2-14 (240)	Gb2-15	Gb2-16	Gb2-17

The 'π' glyph Gb2-14 (half 28) may have a viri sign at its top. This glyph certainly is intended to draw attention. It is flanked by glyphs sharing an undulating sign with Gb5-10:

Gb5-6 (331)	Gb5-7	Gb5-8	Gb5-9
Gb5-10 (335)	Gb5-11	Gb5-12	Gb5-13

If time moves counterclockwise, it will turn a quarter from Gb2-14 to Gb5-10, equal to 5 * 19 = 95 glyphs, maybe indicating the existence of a year with 380 days.