Sample rotation measure fits of the Boomerang. Data at 1420 MHz, 4.85 GHz, 8.35 GHz, and 10.45 GHz were taken at 2﹩\farcm﹩45 resolution. The top two panels show locations on the Boomerang. The area around the three higher frequencies is magnified to demonstrate the accuracy of the fit. The fits for the "tongue" region are displayed in the two bottom panels. A more detailed description is given in the text (§ 3.3).