A standard function that can be used in device classes to set the new sweep value. 'apply' is called by the module of the device class and the new parameter 'self.value' is available when the function 'apply' is called. Please note that 'apply' is only called if the sweep value, i.e. 'self.value', has changed. This prevents that a set value is sent multiple times to an instrument. For example, a repetitive measurement at a voltage of 0 V, only requires to set 0 V at the first measurement point. However, for all subsequent measurement points, sending 0 V is not needed, which is why apply is called again.