Formatting of right hand side of equation should be identical to formatting of left hand side
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block"> <msubsup> <mrow> <mphantom> <mi>z</mi> </mphantom> <mi>S</mi> </mrow> <mi>t</mi> <mn>7</mn> </msubsup> <mo>=</mo> <msubsup> <mi>S</mi> <mi>t</mi> <mn>7</mn> </msubsup> </math>