This tests a range of values for the 'units per em' attribute.
The same glyph is defined three times in three fonts, but with different values for units-per-em - 1,000, 10, and 10,000 - and with the other numerical values that depend on units-per-em scaled accordingly. Text using these fonts must all be displayed at the same size, because the same font-size is used throughout.
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The test is passed if the three letter β are all the same size.