This has been puzzling me for a number of years, I'm sure someone smarter than me knows the answer. If I have a lens with the RX +5.00-5.00 x 45 and I move it 10mm, I understand and expect to induce 2.5 diopters of prism in the horizontal direction. What I don't understand is why the OptiCampus Induced Prism calculator tells me that I also induce the same prism in the vertical direction without moving the lens vertically?

Am I missing something very simple?

Thanks!!
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