Simply turn phorometer handle until horizontal streak bisects white spot of light. Pointer then indicates amount of deviation on red scale. Ignore cases less than 1° hyperphoria, whether right or left designated by (R. H.—L. H.). 3. Place phorometer handle horizontally (Fig. 19). Place red Maddox rod horizontally (Fig. 18). Patient should see a white spot of light and a vertical red streak (Fig. 20). Simply turn phorometer handle until red streak bisects spot of light. Pointer indicates amount of deviation on white scale, whether esophoria or exophoria designated by (Es—Ex). 4. Ignore all exophoria cases, less than 3°. Ignore all esophoria cases, less than 5°—except in children, ignore less than 3° of esophoria. 5. Always make the above or binocular muscle test—with phorometer and red Maddox before optical correction or (test for spheres and cylinders) and again after optical correction where case shows more than 1-3-5 rule, to determine whether muscles are aggravated or benefited. 6. In cases showing more than the 1-3-5 rule, shown in above No. 4, make monocular duction test first with rotary prism before patient’s right eye,—then with rotary prism before left eye to find faulty muscle and determine which eye is affected. 7. To test adduction, prism base out is required. Rotary prism’s red line or indicator should be rotated from zero outwardly. To test abduction, base in is required. Indicator should be rotated inwardly from zero (Fig. 22). Power of adduction as compared with abduction, is normally 3 to 1—usually rated 24 to 8. 8. To test superduction, base down is required. Rotary prism’s line or indicator should be rotated downward from zero. To test subduction, base up is required. Indicator should be rotated upward from zero. Power of superduction as compared with subduction, is normally equal—usually rated 2 for each (Fig. 23). 9. Direct patient’s attention to largest letter on distant chart, usually letter “E,” rotating red line indicator of rotary prism outlined in above No. 7 and No. 8, until diplopia is first procured. 10. The use of a duction chart on a record card, quickly designates pull for each of four muscles (Fig. 24), illustrating an assumed case of— 1st—6D of Exophoria. 2nd—18° adduction (which must be developed to 24°). 3rd—Patient has a left weak internus. 11. Employ First Method—Optical Correction—to effect treatment. 12. Assuming a case of a child with 6° of esophoria—8° of right abduction and 2° left abduction indicating a left weak externus, prescribe a quarter diopter increased plus spherical power for each degree of imbalance, thus adding +1.50D spherical to optical correction. This is the _first_ method of treatment. This requires a thorough reading of Chapter IX on Treatment for Correcting Esophoria in Children and a careful study of the formula. For synopsis see Page 74. FOUR METHODS OF TREATING AN IMBALANCE CASE WHEN THE PRECEDING ONE FAILS 1st—Optical correction;