Address #1156 (comment).

spec/ttml2.xml

@@ -11553,7 +11553,7 @@ images whose processing generates <bibref ref="srgb"/> pixel values, and an abso
 only the <bibref ref="srgb"/> pixel values are transformed.</p></note>
 <p>When applying <att>tts:luminanceGain</att>, the linear optical output values
 (C<sub>r</sub>, C<sub>g</sub>, C<sub>b</sub>) of the <loc href="#terms-component">components</loc> of a pixel of a region are defined as
-80 cd m<sup>-2</sup> ∙ <att>tts:luminanceGain</att> ∙ (r, g, b), where (r, g, b) are the normalized linear <bibref ref="srgb"/> <loc href="#terms-component">components</loc> of the pixel.
+80 ∙ <att>tts:luminanceGain</att> ∙ (r, g, b), where (r, g, b) are the normalized linear <bibref ref="srgb"/> <loc href="#terms-component">components</loc> of the pixel.
 </p>
 <p>If a computed value of the property associated with this attribute is not supported,
 then a <loc href="#terms-presentation-processor">presentation processor</loc> must use the closest supported value.</p>