Used to hang a safety clip ball compass off the front of my handlebar bag .. But

if you want more than a gimmick, take a compass and your paper map,
And walk well away from steel things..

so best is the one to put in the chart /map case..


Steel Ships have the Binnacle Kelvin/navigator's balls http://en.wikipedia.org/wiki/Binnacle
to compensate for the ship around the compass..