Syriac letters double as figures on a simple plan inherited with the alphabet. The first nine letters carry the units, one to nine. The next nine carry the tens, twenty to ninety, with yudh at ten. The last four carry the hundreds, one hundred to four hundred. Sadhe closes the second group at ninety, and qaph opens the third at one hundred.
The design has a consequence that is easy to miss: the alphabet runs out. Twenty-two letters reach four hundred and no further, so anything above that is written by combining letters, or by marking a letter to multiply its value. A mark below a letter serves for the multiplication. The system is workable rather than elegant, and it was never meant to carry arithmetic; it was meant to write down a number that has already been arrived at.
In practice it does that constantly in Syriac manuscripts. Scribes number the leaves and quires of a codex with it, which is what lets a book that has lost its binding be reassembled and a missing quire be identified as missing. Dates, chapter divisions and marginal references use it too.
The same scheme, with the same values at the same places, runs in Hebrew and, through the abjad order, in Arabic, because all three inherited it with the sequence. Comparing the three at the point where the tens end is one of the clearest demonstrations that the sequence itself is the thing being inherited.