My understanding is that it’s only an upside-down inversion. I could only find two crappy links on the subject, though. 1 2
ETA: Page 4 of this paper.pdf) refers to both horizontal and vertical inversion goggles.
My understanding is that it’s only an upside-down inversion. I could only find two crappy links on the subject, though. 1 2
ETA: Page 4 of this paper.pdf) refers to both horizontal and vertical inversion goggles.