An apparatus and method are provided for the dynamic instrumentation of code to minimize system perturbation during tracing of the execution of the code. The knife holder 13 is separated into a fixing member 17 mounted onto the cutter shaft 6 and a mounting member 18 onto which the knives 15 are mounted. The controller is to control switching of the switches to deliver the power to the load to reduce perceptible flickering of one or more lights coupled to the power source. A projection of the first radiating patch on the ground conductor is located on one side of a projection of the shorting patch on the ground conductor.