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Humidity
I can't stress this enough , without good control of RH in the shop , it will limit your building time and worse cause problems for your guitar down the road. There are many ways to control this but without a good hygrometer to measure it you are at best guessing.
I have yet to find a digital one that was accurate under $50. I use abbeon. It is lab rated and calibrated when you get it. Please do yourself a favor and learn how to do this. It is as important and learning how to make a good joint.

40% to 50% is ideal, danger areas are under 35% and over 60%.

lets hear how others control RH in their shops

Which one of these are you using?

http://www.abbeon.com/Item--i-digitalpo ... hygrometer

http://www.davis.com/Product/Humidity_a ... 7Aod0XAABw
this is the one I have.

I can attest that improper humidity will cause problems. The back of my guitar is essentially flat, even though I built a 15' radius into it. I got the rough-shaped radiused back braces from my luthier, who of course has humidity control in his shop. (He has the same gauge you do, John.) I glued the braces onto the back in my own shop, which has no control. Whatever the combination of circumstances, the back curvature has almost totally disappeared.

My work area is at 33% rel. hum. causing the three bodies I've been working on to look like raisins. Dead flat and one even slightly dished. (Got them bagged and re-hydrated now.)

I used to build at 10-20% when I lived further north. Never had any issues until coming to the mid-Atlantic region with its humid summers.

I'm curious to find out what will happen to my guitar this summer when the humidity gets to the "you can see the air" stage.

Many of us can't justify the expense of an Abbeon or other good hygrometers but need to monitor and maintain RH. Two suggestions:

1. Any hygrometer (I use my Samsung Galaxy S4 mobile phone and the Android app "Weather Station) can be validated with Potassium Carbonate and a small amount of distilled water. A few tablespoons of Potassium Carbonate saturated with water in a small open container (baby food jar) placed in a heavy ziplock along with your hygrometer will produce a 43% RH microenvironment at room temperature if allowed to sit overnight. Notice the difference between the hygrometer readout and 43%. Add to or subtract from future readings the hygrometer makes around 43%. Sources for Potassium Carbonate: http://www.soapgoods.com/potassium-carbonate-p-719.html or http://www.amazon.com/Potassium-Carbona ... +CARBONATE If you want to validate your hygrometer for a higher or lower RHs you'll need some Kosher salt and distilled water used as above for a 75%RH control and a Boveda 32%RH Calibration Kit http://www.amazon.com/Boveda-Low-RH-One ... WEZGGJKZ3B

2. If #1 is too complicated, the gold standard for the measurement of RH is comparing the room air temperature ("Dry Bulb") with the "Wet Bulb" temperature. The wet bulb temperature is the temperature of evaporating water from a wet cloth tube (like part of a tennis shoe string) which surrounds the bulb of a thermometer. The wet bulb thermometer is slung around in the air attached to a cord until the temperature stabilizes. The lower the humidity, the colder the "wet" temp. That number is used in a chart or computer program/spreadsheet (http://andrew.rsmas.miami.edu/bmcnoldy/Humidity.html) along with the "dry bulb" temp and barometric pressure to calculate the humidity. You can also position the wet bulb setup in front of a fan and watch the temperature drop and achieve the same result as slinging it.

Another related cost saving idea: If you work in an area with an unsealed concrete floor, the floor can be used as a humidifier by pouring a few quarts of water around your bench and in front of any heaters before you start working and when you leave for the night. The concrete will absorb the water and slowly release it. Pay attention to the RH and increase/decrease the amount of water. Use common sense with electric tools and standing in water, yadda, yadda.

yes that is true learning to calibrate your hygrometer is very important. On the other side of the scale is the higher humidity , then you need a dehumidifier. I have to run 2 in my shop one up stairs and one down stairs. I use a 70 pint downstairs and a 40 pint up stairs.
too wet can be as damaging as too dry.

http://www.hoskin.ca/catalog/images/psych.jpg
This is what I use.
Tom