NavList:

With all the talk about backlash and turning the micrometer drum in one direction I started thinking. I figured that with tapered thread forms, spring loaded against the sextant arc, there would not be very much backlash at all.

So I set up my trusty Harbor Freight dial indicator agaisnt the index arm on an my Ogawa Seiki sextant. I turned the micrometer drum slowly until it lined up with a minute mark on the drum at the index mark. I then reversed the drum direction, watching the dial indicator to see if there was any backlash to be taken up, before the dial indicator needle moved. The conclusion was, there was practically no backlash, the dial indicator seemed to respond very nearly immediately to a reversal of the drum direction. I tried to measure the drum rotation necessary to move the needle on the indicator and found that a movement on the drum of less than 0.1 minute caused the dial indicator to respond.

Just thought I would share this.