Syriac is written in three hands, and the difference between them is a matter of history rather than of the alphabet. Estrangela is the oldest, a formal book hand used for scripture and for inscriptions, and it is the hand in which the earliest surviving Syriac was written. From it developed Serto, the western hand of the Syriac Orthodox, Syriac Catholic and Maronite churches, and Madnhaya, the eastern hand of the Assyrian Church of the East and the Chaldean Catholic Church. All three write the same twenty-two letters in the same order with the same numeral values.
He is a good letter on which to see the divergence, because its Estrangela form is a compact closed loop and the later hands redraw it substantially. A reader trained on one hand does not automatically read another, and learning Syriac in practice means learning to read at least two.
The split is not only calligraphic. The two later hands carry different vowel systems, the eastern using dots and the western using small Greek letters, and different traditions of pronunciation, so a text read aloud in the west and in the east does not sound the same. The consonantal skeleton on the page is what they share.
An entry in this atlas for a Syriac letter is an entry for that shared thing: the letter of the abjad, which each hand draws in its own way, and which no one hand owns. Where a statement is true of only one hand, it is said so.