Quarterly moving mean

The quarterly moving mean for the data in Figure 2.5.7 is illustrated in Figure 2.5.9. Note that it is usual to plot both the actual monthly figures as well as the moving mean, and this has been done in Figure 2.5.9. 

Figure 2.5.9 Monthly accidents and quarterly moving mean (2001)...

For many applications, there may be some advantage in employing phase modulation 54,85) instead of the usual amphtude modulation. In the latter technique the path of the radiation from the source to the detector is blocked and opened periodically by a chopper (cf. Fig. 20 and Section 4.3). For phase modulation, the chopper is removed from the spectrometer and the fixed mirror of the Michelson interferometer is moved back and forth about its mean position with a certain frequency. In contrast to the interference modulation (see Section 4.2), the amplitude of the mirror motion is small, being a quarter of the wavelength of the light. For the analogue Fourier transform or interference modulation, the amplitude of the mirror has to have many wavelengths in order to achieve a reasonable resolution... 

A wrench for removing patent breeches or nute bom double guns is made like fig. 13 U consists of a steel bar about fifteen or sixtcon inches long and about three-quarters of an incl) diameter. At a little to one side of the center is fastened a steel collar that has four projections made at one end. A similar piece is fitted opposite to it, bub is made to move back and forth to fit tlie work by means of a acrew that is fotmed behind where it is fitted. A dot is made in tlie extension of the piece and a key fitted to prevent its turning around as b)ie nut is turned to advance it toward lls fellow piece. 

On examining the face of the disc D, to which the telescope is attached, it will be seen that it is graduated over a quarter of its circumference into degrees and half-degrees (30 ) and there is a vernier with thirty divisions, by means of which single minutes can be read. The reading of the vernier is facilitated by a small lens, which can be moved in front of the scale. For the purpose of making fine adjustments, the disc is fixed by means of the screw H, and the fine adjustment made by means of the screw G. 

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