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A similar secret method of indicating numbers we find also in some instances in old Siamese Mss. The method goes by the name of aksara saṅkhyā, the numeral letters. By its name its Indian origin is shown.
We find no indication at what time the system has been introduced and, although as regards secret writing it would lend itself to many combination, it seems mostly to have been employed in astrological works.
The letter which are used for the forming of figures are those of the Indian alphabet and none of the specific Siamese letters enter into the combination⟨.⟩ This alphabet is divided into three divisions of nine letters each called navasaṅkhyā, and the vowels with ñ and n for zero called sūnasaṅkhyā:—
We have thus to indicate the numbers from 1–9 the following
| ก | ข | ค | ฆ | ง | จ | ฉ | ช | ฌ | ||||||||
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | ||||||||
| ฎ | ฐ | ฒ | ฑ | ณ | ต | ถ | ท | ธ | ||||||||
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | ||||||||
| ย | ร | ล | ว | ส | ศ | ษ | ห | ฬ | ||||||||
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
and further to indicate the numbers from 1–5
| ป | ผ | พ | ภ | ม | ||||
| 1 | 2 | 3 | 4 | 5 |
Whilst for Zero we have the vowels
| อ | อา | อิ | อี | อุ | อู | เอ | โอ | and | ญ | น | ||||||||||
| ๐ | ๐ | ๐ | ๐ | ๐ | ๐ | ๐ | ๐ | ๐ | ๐ |
The example is:—
| อายุ | ประมาณ | ก, | ญ, | น, | ปี | เปน | ค, | อ, | อา, | ฤดู | ||||||||||
| ๑ | ๐ | ๐ | ๓ | ๐ | ๐ |
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