When the base level reading of the RS meter is 5mph you are giving away 25-30 inches of drift at 1000yds before you can even begin to measure. A one mph error is 5-6 inches. This error is one top of other unknown wind drifts. Go see Shawn's post on the 338 edge vs the steel plate and look at his shooting lane. He is buffered by trees at the shooting point which reduces the measured velocity and very quickly the bullet will break out into open space where the true winds will hit it. Also, there are two winds in a canyon that you have to guess at. One is the vertical thermals and the other is the morning or evening downflow or upflow. Finally, there is the wind at the target site. At the target site, if you have good glass you can watch the vegatation to "guess" what it is. Then there is the wind angle which can be murderous. Where I hunt, there are vortexes formed by the river bends that range from a few hundred yards to a mile in diameter. My point is a wind meter
gives you the most important wind which is the one at the barrel and all the rest are up to you to judge based upon that one data point. When you don't have that data point you just lick your finger and hold it up.
The radio shack is a good entry level wind meter that will help you a lot but when you get the perfect conditions early in the morning or late in the evening and just a little temperature induced canyon wind such as what Shawn had, your RS wind meter is not going to be of any help.
At closer ranges such as 500 yds small wind values are less important except for shooting at very small targets.