Abstract: A friction testing positioning device (10) comprises a first wheel (12) rotatably mounted around a first axis (14) at a first end section of a transmission arm (16), said transmission arm (16) being pivotably mounted around a second axis (18), at least one second wheel (20) rotatably mounted around a third axis (22) at a second end of said transmission arm (16) and a transmission means (24) connecting said first axis (14) and said third axis (22), wherein said at least one second wheel (20) engages a substructure (26) and said first wheel (12) and said at least one second wheel (20) are being arranged to rotate at different speeds of rotation. A first vertically adjustable displacement means (28) operates on said transmission arm (16) to rotate around said second axis (18) and to press said first wheel (12) into engagement with said substructure at a substantially constant vertical force.

Abstract: An electrical heating pad, in particular a mattress to be placed under a patient during surgery, comprising a number of partially overlapping resistor elements (11-18). The foil elements cover different regions of the pad and are positioned in an overlapping configuration such that in substantially all portions of the pad there are at least two overlapping foil element parts. Each foil element is fed separately from control circuitry so as to maintain a uniform temperature at all portions of the pad, irrespective of the heating load at different portions.