How do you set the time to the Nixon 51-30 watch. Also what can you do to stop the knob from coming all the way off when unscrewed?

click link below for the manual, Be passant it takes a while to download..
http://demandware.edgesuite.net/aayf_prd/on/demandware.static/-/Sites-masterCatalog_Nixon/default/dwe2d7f3fa/manuals/nixon-unit-dive.pdf

hoping this would be helpful.
Nixon Watch The Lodown Setting the Time Tide Location

Pinch the shaft from the inside and unscrew the crown

Hi here is the link for all of the nixon manuals
http://www.nixon.com/manuals/index3.html

Kind regards

Try this:
Resetting Chronograph Hands:
Note: Some Nixon watches come equipped with a "screw-down" crown; the crown must be unscrewed by turning it counterclockwise before it can be pulled out)
1. Pull the crown all the way out to position 2.
2. Push the crown in slightly to position 1.
3. Push top pusher button to advance the second hand to line up with the 12:00 position
4. Push the crown back in. (Make sure it is screwed in if it is a screw crown)

It may just be a coincidence that the battery is dead at the same time you changed the hours

This is not done in the alarm section. In the time view, press and hold the wave#/reset button (lower right) until it beeps (3 seconds). That's it. The watch should be silent now when cycling through and on the hour.

Follow this link: http://www.nixonnow.com/manuals/index2.html This is all what NIXON is offering for download. Rate me, plz.

Visit: www.nixonnow.com/manuals/nixon_analog.pdf

Pull the stem all the way out...like your setting the date. Then hit the upper button and that will move the hand 1 second at a time until it gets here you want.