Mirror ruler

The earliest method for the differentiation of spectra or other signals, the graphical method, is only suitable for simple curves furthermore, it requires a great deal of time. The tangents are best drawn by a mirror ruler (Fig. 3-1). The ruler must be positioned in such a way that the mirror-image shows the curve without a break then the tangent is drawn rectangular to the direction of the ruler. 

FIGURE 3.55 Photograph of a capillary-column toolkit containing tweezers, needle files, scoring tool, pin vise drill kit, flow calculator, pocket mirror, miniflashlight, labels, septum puller, stainless-steel ruler, and pipe cleaners (reprinted with permission of Supelco, Bellefonte, PA). 

This is further signified by the fact that these four players were most likely sacrificed - not to demonstrate the ability of a ruler to dispose of people as he pleased, a show of his absolute power over life and death, but to provide the bodies necessary to play out this scene. Hints as to just why this was done lie in the stratigraphic sequence of events and the patterning of its composition, which in all its detail accomplishes one very specific scenario mirroring. 

---