inducing prism question

[optik]

Hi
I need to induce 1.5BU but at 5mm above the center. I calculated that a -4D lens decentered 5 mm will give 2D prism. So I dotted the lens at .5BD thinking that when I blocked it at 5 above I would wind up w/ 1.5BU . it didn't work - where did I go wrong ?

Thanks !

[newguyaroundhere]

Blocking a lens 5 mm above center results in 2 diopters of base down prism, not base up

[newguyaroundhere]

http://www.opticampus.com/tools/induced.php

[MakeOptics]

Put your lens in the lensometer and mark the lens at 1.5BU, then layout the lens when blocking 5mm above center.