I've got two Tilts going right now. Both are in the same base juice for hard cider. One batch is in a 3 gallon glass carboy, the other is in a standard plastic fermenting bucket. Pitched with different yeasts. I got the juice fresh off the press, and it measured 1.056 (temp corrected) at that time. My home hydrometer and refractometer both read 1.057 the next day. I did a water cal with the Tilts, but didn't cal them in the juice when I first added them. One read 1.057, the other read 1.058 (1.057 uncal), so I just let them go. I'm using the Google Docs export function to track activity, and probably could have done a little more before hand if I had thought about running some experiments with the Tilts.
Yeast was pitched a day and a half ago, fermenting room is right about 64F. Cal temp for the Tilts was 65F.
Fermentation had been slow to start, with just a little airlock activity on the bucket when I left the house at 06:30 this morning. Looks like it really kicked off around 08:00! Both Tilts have and SG and temp increase, peaking between 9-9:30. Especially in the 3 gal carboy. Temperature ramped up from 65.0 to 70.0 and SG peaked at 1.081. Temp has dropped back to 69.1 and holding for the past 3 hours, and SG has fallen to 1.068. The 5gal bucket peaked at 1.079 overnight, but didn't have the temp ramp until this morning. It's now down to 1.058, on a trend of falling .001 per hour.
I'm guessing it will settle out over time. I wasn't planning on opening up the fermenters until ready for secondary, so I haven't measured with a hydrometer for comparison.
From the Tilt FAQ:
Q. How do bubbles from CO2 affect the Tilt?
A. We recommend putting the Tilt in your beer prior to pitching yeast, this will ensure any bubbles will not affect initial readings. Bubbles from dissolved CO2 may cause higher than expected readings for a short time if placed in an active fermenting brew. However, this can be sped up if washed with alcohol (i.e. Everclear).