I called Brinsea customer service (twice). As per her instructions I removed the bulb thermometer and heated it to make sure there were no bubbles in the column from shipping. I decided, while it was out, to calibrate it against some other thermometers.
I placed 2 oral digital thermometers with the Brinsea in a glass and placed very hot (108 degree F) water in. With all the tips close together, I took readings as the water cooled. The glass thermometer was off by an average of 5.4 degrees. The two oral thermometers were 0.3 to 0.2 degrees off from each other through the whole range. When the bulb thermometer reads 99, it really is 104.4-ish inside.
Turned it down a full half--turn on the red knob (=4 degrees) and it seems to be stable at about 100.0 degrees. Good enough. I'd be really upset if I cooked my expensive Cream Legbar eggs at 104 degrees! Goes to show you can't rely on anything without verification.
Brinsea said they would ship me out a new bulb thermometer on Tuesday since the one with the unit must have been damaged in transit. Great customer service.