As part of mandated yearly performance evaluations on over 120 GE, Siemens, Philips and Toshiba 1.5T scanners, the ACR phantom was used to make 2555 measurements of RF slice profiles and thicknesses. Aggregated slice profiles are plotted showing clear differences between vendors both in terms of ‘squareness’ and FWHM thickness. With a target slice thickness of 5.0 mm the measured thicknesses ranged from 4.21 to 6.65 mm! The affect that interslice gap has on measured profiles (RF crosstalk) is demonstrated for T1 weighted sequences. A very surprising dependence of measured thickness on slice position on the ACR phantom is demonstrated.