Although a century later than the Voynich, it is still curious that some astronomical tables use a similar glyph such as the slash. These are the Prussian tables of Erasmus Reinhold, which replaced the Alfonsine tables.
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Here you can see a page from an edition of the Prussian tables with the slash to indicate parts of the circle of the elliptic. Interestingly, the slash is also repeated like the Voynich glyph.