The 563 scale level is a very handy tool which attaches directly to your optical tooling scale, having two bull's eye vials mounted at right angles. This allows you to orient your scale either horizontally or vertically. The level is sufficiently sensitive to allow you to keep any significant cosine error from creeping into your scale readings. A knurled thumbscrew tightens an angled dovetail bracket against the side of the scale, holding it firmly against the reference edge of the level.
The scale level may be placed at any convenient place along the length of the scale. The 563 fits any of our scales having a width of 1" (3" to 20" scales).