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Curv* pottamt

Principles

1. The purpose of multiple omounl scoles is to compere the movements of two or more series differing considerably in magnitude.

2. Multiple omount scales can be effectively used for comparing on the same grid two or more series not measured in comporable units (e.g., dollars and tons}.

3. In general, the use of multiple amount scales should be restricted and regarded as a device for special cases.

Procedures

1. LIMITED NUMBER DESIRABLE. Multiple scales should normolly be limited to two, as more ore likely to be confusing.

2. SAME RULINGS FOR BOTH SCALES. Scales should be so selected that all horizontal rulings for both scales will coincide.

3. ZERO VALUES SHOULD APPEAR. The zero lines of both scales should, if possible, be included on the chart and should coincide.

4. WHEN ZERO IS OMITTED. If the zero lines of the two scales cannot well be shown on the chart, the scales should be so adjusted that the zero lines would coincide if the scales were extended to zero. This procedure, illustrated at the right, will present the curves in their correct relationship.

5. CONTROLLING CURVE MOVEMENT. Scales should be selected which will ovoid undue emphosis of any one curve. iSo selected that the relative movement of the various curves will be comporoble. It is not permissible to enlarge the movement of one curve orbitronly while minimizing the movement of the other.)

6. WIDE SEPARATION UNDESIRABLE. Scales should be selected that will bring the curves in close enough proximity for ready comparison.