The OH-2+ is the latest version in the OH-2 hygrometer product line. It has a new digital sensor that im-proves the accuracy of the hygrometer to +/- 3% between 20% – 80% RH. The hygrometer also has an ex-tended reading range down to 10% RH rather the 20% RH on the previous two models. This eliminates the annoying “LL” sign one the display when the humidity drops below 20% RH. The increased range will help those users in extremely dry areas to get a more accurate reading of their humidity.The humidifier has the same size and look as previous versions. The calibration feature is also included, but shouldn’t be necessary with the improved accuracy.Don’t forget the OH-20 hygrometer holder that allows you to place the hygrometer near the sound hole for accurate RH readings.