= Mathematical typesetting axis
= Math axis
{synonym}
The \b[mathematical typesetting axis], or <Math axis>, is a horizontal alignment reference for a formula. Its offset from the <text baseline> is a <mathematical font constant>, represented by `axisHeight` in an <OpenType MATH table>.<MATH - The Mathematical Typesetting Table by Microsoft>[MathConstants: axisHeight and baseline offset]{ref}
For an invented coordinate example, choose upward-positive coordinates, put the <text baseline> at $y=0$, and set the axis offset to $a=250$ <font units> in a <computer font> with 1000 <font units> per <em>. At 20 <pixels per em>, the axis is $250(20/1000)=5$ <pixels> above that baseline. A symmetric enclosing shape spanning $y=-350$ to $y=850$ has midpoint $250$, so its centre lies on the axis.
The <typeset fraction> bar is another useful alignment cue. The reference fixes relative placement; translating the whole formula also translates its baseline and axis.
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