I agree with the comment that if you get with in 10 feet it is good. It is like hand grenades or horse shoes, if you get it close it is effective.
When I hide a cache, I usually find a good hiding place and then take a reading. If terrain and vegitation lets me I walk 50 ft from the site. I will do this four times in each direction of the compass. When I return to the cache site I take reading. So when I am done I have 5 readings. I average the five and that is coordinates I use.
Half fun is finding the hiding place.