I have been useing a Dell Axim 30 with the Exbal Ballistics Targeting Software from Nightforce. This worked well for me for a couple of years. A while back the system lost part of the program and I decided to updata to a more rugged system. That were the TDS Nomad came in, this is a powerful small computer with an 806 MHz processor, Bluetooth compatible with a GPS system integrated in, and wireless internet compatible.
I purchased this unit from Ken Pratt at Nightforce with the Exball program installed and ready to go as soon as I received the unit. I went with the Nomad model and by passed a Laptop that I was planning on purchasing. This unit can do anything that a laptop can, yet it is much smaller and much more portable.
The Kestrell is showing 30.02 inches of mercury at sea level, with this imput into the Nomad I can get very accurate field data on the spot.
TDS Tripod Data Systems: TDS Nomad: Overview
Also there are available Topo maps programs that are down loadable for this unit
Main - BackCountry Navigator
Check out this site to see exactly how rugged this unit is, they even run over it with a pickup truck,
range it,check the wind, dial in correction, aim and only one shot