A bi-directional communications interface includes a source multiplexer for connecting to a video source. It is the object of the invention to provide a protective device for microscopes of the type described above which ensures protection against eye damage and visibility of the sample. The air flow device issues an air flow rate signal indicative of at least the actual air flow rate and receives an air flow control signal. The status of the subject, and in particular, the presence andor absence of the one or more conditions, can then be determined in accordance with the results of the comparison. The yoked prismatic glasses are adapted to stimulate inhibitory and initiatory areas, respectively, of the wearer’s visual cortex and, thereby improve visual disorders relating to behavioral visual blockage patterns. A finishing pan is provided to finish the concrete surface.