An apparatus for monitoring the exhaust of an engine includes a flow-through chamber for receiving exhaust, a source of electromagnetic radiation and a detector. Said recesses have a rounding-off encompassing, along the rounding-off, at least a first portion with a first radius of curvature, a second portion with a second radius of curvature and a third portion with a third radius of curvature. A tool securing bar having a generally triangular shape in the bar’s middle section forces the arris-defining back of the tool being honed against a reference surface in the guide by tightening thumb nuts around threaded studs projecting from the bar. Context may be relationships defined for displaying a timeline event within a layout and visualization scheme such as size of the timeline element, display relationship with respect to a timeline, display relationship with respect to levels or containers, and display relationship with respect to other timeline events. Among the RGB field images, the G field image having highest spectral luminous efficiency is displayed at an intermediate order within the frame images so that leakage thereof is not caused by the pixel shifting operation.