A feature of the recording device is used to shorten the length of time that a wireless communication link with a recording device is not established for a control device that communicates wirelessly with a recording device when a wireless communication link can be established. A pressure canal for hydraulic transmission of pressure to a measuring cell, includes, for dynamic overload protection, a Venturi throttle implemented by providing that the pressure canal has at least one segment whose flow cross section is variable. From the edge profile a blurring value is estimated for each frame or group of frames within the test video sequence. Raised ribs extending generally perpendicularly outward from the rear surface of the fin blade inter-connect, providing a stop mechanism to retain the blade in a generally rigid configuration on power kicks in the direction of its front surface.