II. CYCLOGRAM ANALYSIS 



GRAPHIC EXPRESSION OF DATA 



Definitions — During this study of cycles and the development of a new 

 method of their determination, the meaning of certain special words has 

 suffered some modification. So in the somewhat unfamiliar paths of cycle 

 study, it is well to clear the way by a brief review of several semi-standardized 

 expressions for use in subsequent description, and not as an exhaustive study 

 of technical words. 



An "extended" curve is one that represents an unbroken series of data 

 through a succession of equal intervals of time. Such curves may take the 

 following forms: 



A. Unmodified or Primary Curves 



1. "Original" data, unmodified by special treatment. 



a. Columnar plot. 



b. Point plot. 



B. Modified or Secondary Curves 



2. "Smoothed" curves. 



a. Running means. 



b. Hanned curve, or weighted running mean, sometimes called 



second or fourth intermediates. 



3. Mass diagrams and residual mass diagrams. 



4. Logarithmic plots. 



5. Skeleton and increment plots (simplified curves). 



6. Standardized and equalized curves. 



7. Merged curves. 



8. Compressed curves (a technique for handling long series of data). 



9. Curve character figure; mean sensitivity. 



10. Curve comparisons; correlation coefficient. 



11. Curve summaries; the periodogram. 



Original Data — Original or primary data are data that are unaltered; 

 these words distinguish them from integrated or summated data (see below) 

 or mass or smoothed or otherwise secondary expressions of data. The original 

 plot, which gives a series of values at definite time intervals, may be columnar 

 or point, illustrated in figure 6. The latter is the common form but neither 

 is perfect. The columnar plot emphasizes only one value during the time 

 interval between plotted points. This interval is one year in most of our 

 curves. In tree-growth plots, this is accurate, for only one value is com- 

 monly measured for the year. But in rainfall it is less satisfactory as the 

 known monthly variations are lost sight of. The common plot with lines 

 drawn from point to point clips off the corners of the columns and suggests 



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