The Brunton Sherpa works Very well, however it does not deliver a humidity reading (not that that matters ~ but it is part of the equation in most if not all software packages). The Kestrel
's 3500 and 4000 do. I have had one of those for approximately four years and it has worked exceptionally well. I once tested a Speed Master just like the one Ian has. It worked just fine, however (at the time) it only functioned in metric units. If I were to rate them, the Kestrelís would rate 1st, then the Brunton Sherpa followed by the Speedmaster.