An apparatus includes an operational amplifier circuit comprising at least one operational amplifier and a feedback circuit coupled between the output terminal and input terminal of the operational amplifier circuit and configured to apply a feedback gain to an output signal at the output of the first operational amplifier. The guide rods 2 receive, from twist coil springs 5 fitted to a chassis, an elastic restoring force and are thereby loaded with a force that tends to move the guide rods 2 away from the recording surface of the optical disc. When a problem is reported, a similar technique causes the machines to collectively evaluate and report suggested causes for that problem. The Kalman filters can fuse the outputs from the stationary array sensor and the scanning sensor to track, and compensate, drift of the stationary array sensor. Selective engagement is by contact between corresponding protrusions on the delay and locking cams. A mixture of 8-carbon and 9-carbon hydrocarbons which are typically primarily paraffins or cycloparaffins typically makes up the vast majority of the petroleum distillate.