Tibetan Digit Half Zero

Unicode reads it as minus one-half. In Unicode 17.0, Tibetan half-digits can appear only as the final digit of a multi-digit number; each is 0.5 less than its matching whole digit, so half-zero is negative one-half.

Is ༳ a crossed-out zero?

No; it is a complete Tibetan numeral with a hooked slash. A report from 2000 says ༪ marked half a unit in plans showing the proportions of Buddha figures, temples, and mandalas (sacred diagrams). It also relays an account that crossed digits in Tibetan astronomical and astrological calculations were calculation marks, not fractions. Unicode 17.0 describes the half-digits as not well attested.

A 1995 proposal for encoding Tibetan used a separate slash mark combined with digits; the eventual design gave each half-digit its own character. A 1933 postage stamp uses sibling ༱, half-eight, for 7½ skar, a Tibetan monetary unit. It supports a fractional use for the set, but does not show ༳.