Tawe writes a plain t and continues the Semitic consonant behind the Hebrew tav, the Syriac taw and the Arabic ta. In the Northwest Semitic order that letter stands last, and the phrase from aleph to tav is the Hebrew equivalent of from A to Z. In the halehame order tawe is tenth, and no such phrase is available, because the order ends elsewhere.
Ge'ez has a second t letter, tayt, which writes the ejective. The pair is inherited: the same distinction exists in Hebrew between tav and tet, in Syriac between taw and teth, and in Arabic between ta and its emphatic counterpart. What differs is how the second member is made. In Ge'ez it is an ejective. In Arabic it is pharyngealised. In Hebrew as read today the two have fallen together and the difference is only orthographic.
So this letter and its partner make a useful test of what a script preserves. All four alphabets kept two signs. Two of the four languages kept two sounds, and they did not keep the same two sounds. A letter is evidence that a distinction once existed, not that it is still made, and reading a fidel chart as a phonetic description of modern Ethiopian speech gets that the wrong way round.
The same caution applies to the vowel orders. Seven orders imply seven vowels, and the classical language is reconstructed with seven, but the values given to them in the received reading tradition are not identical to the reconstructed ones. A chart records a system of contrasts. What a listener hears when the chart is recited aloud is a later settlement of that system, arrived at over centuries.