Aligning Cursors on Duplex Slide Rules
First, Align the Slide Rule Stators and Adjust the Sliding Friction on
the Slide. Ignoring the cursor for the moment, loosen both body
screws. Align the scales on the top stator, the (middle) slide, and
the bottom stator. (For example: If the A scale is on the top
stator and the B scale is on the slide, align them so they match exactly;
similarly, if the C scale is on the slide and the D scale is on the bottom
stator, align them while holding the A and B scales in alignment. Re-tighten
the body screws. Check to make sure the slide works as you want it;
if it’s too loose or too tight, redo the stators.
Loosen all eight cursor screws one or two turns.
Align One Hairline. There is a cursor spring attached to one
of the cursor bars. We’re going to call this bar the “spring
bar” and the other one the “nospring bar.” It’s the nospring bar that
we’re going to work with. Hold the nospring bar firmly against the
edge of the rule. Pick a window and frame—either one, it makes no difference.
We’re going to call the window and frame you choose the “first window.”
Arrange your first window so that the hairline covers the left indices on
the “A” and “D” scales at the same time. (Or crosses any scale from
the top stator with its corresponding point on a scale on the bottom stator.)
Tighten the two screws that hold that first window to the nospring cursor
bar. That first hairline is now perfectly perpendicular to the
slide rule. Leave the other six cursor screws loose for the moment.
Adjust Cursor Sliding Tension. Now adjust the tension on the cursor
by pressing the spring cursor bar against the body of the rule. When
the cursor slides about right, tighten the remaining two screws on the first
window. You are now finished with the first window. Its hairline
should straight across the rule, both bars should be firmly attached to the
first window and the cursor sliding friction should be correct.
Align Second Window Hairline. Set the cursor so your first window
hairline crosses all the left indices on the A, B, C etc scales. Turn
the rule over (don’t jostle the cursor) and work on the second window.
It needs two adjustments: (1) Make sure it is exactly opposite the hairline
on the first window on the other side of the rule. (2) Make sure the
second hairline is exactly perpendicular to the body of the rule so that
the hairline crosses all indices simultaneously. It’s fiddly work.
When you think you have it right tighten the two screws in the nospring cursor
bar. Check your work; if everything seems OK, tighten the last
two screws in the spring bar. Congratulations.