Salem

Now im searching for higher purity mines, but i got some problem about how the drowsing work:
as the purity of my rods increasing, i can find fewer mines,so now maybe i need to spend hours to find a potential high mine,so most of the time, my arrow spinning 360 degree around me, but i noticed sometime it spins very fast, sometime its slow, is there any hint to use this to find mines more efficientely??

Yes, use kandarim's client.

basically, if the arrow does complete turns over your head (i.e. larger than 360 degrees), you haven't got a mine in your range. If you have a detected mine, the arrow will only cover a pie slice of the angle interval (even if it can be very large, e.g. 300 degrees or something). My preferred method of prospecting is a simple gradient search:

run until you detect a mine
keep running until the angle starts to increase again.
head orthogonal to your current direction, either to the left or the right, whichever decreases the angle.
Rinse and repeat.

This is iron node found with 0% wand
http://game.salemthegame.com/mt/ss/6c88b85a7120f15ac07ed3d72cae0b6f
This is nothing found with 12% rods at the same place
http://game.salemthegame.com/mt/ss/b5c2f350d2a45a6000b46833350d373f
Any idea?

Afaik you cant see mine if its stats (salt itc) is more then +/-10 from dowsing stats. Probably your 12% rods got too much of something to detect this mine.

Bingo!
Thanks!

rods/wands can only detect mines which are "close" to their own elemental make-up (unsure about the interval width).

ffr: there was a bug at the start of the providence server where wands could find ALL mines, but this has since been fixed.