Update on April 2, 2008:
I worked in the shop for a few hours with two windows partially open, one day after a good, steady rain that lasted several hours. One hour after opening the windows the relative humidity (%RH) was up to 46%. The base and the remote units reacted nicely, to let me know the shop %RH is going in the right direction – the number of heating hours is greatly reduced with the arrival of Spring.
With the end of the heating season, the relative humidity (%RH) in the shop is slowly going up, as reflected in the readings with the inexpensive thermo-hygrometer I purchased a while back. This is a reflection that the furnace has not been running as much in the last two weeks, due to warmer weather; plus we have had some rain, and Spring has (finally) arrived!
As you can see in the images below, %RH is now in the 30s. This is a significant increase from the 22% RH of early March, when I first received the unit and started monitoring, but still too dry.
I placed the remote wireless unit on the lumber rack, located less than 2 feet from the overhead door, and about 35 feet away from the base unit. The remote system has consistently indicated 2-3% higher RH than the base unit; I placed the base unit 10 feet away from the air handling room, and about 15 feet away from the nearest outer walls on the shop.
This discrepancy is interesting, as initial testing in the house, with the units only 6 inches or so apart, showed a discrepancy of only 1%RH. I can speculate that the current discrepancy is real, as some wind enters the shop via the overhead door (close to the remote unit), while the base unit sees mostly the slightly drier air near the furnace.
I am very pleased with the early monitoring results; this compact system has confirmed initial suspicions about the air in the shop being too dry. As you know, other work kept me out of the shop for over a week. But I used the Memory key (on the bottom-right corner of the base unit), and it showed 36% RH as the highest reading since I started monitoring.
One last thing: The absolute readings become less critical in actual monitoring, as environmental conditions around each of the monitoring units may be in a more or less humid area. What is important is to know how close to each other the readings are before starting to monitor a large volume, such as your shop.