Cut-off in fractions of stroke Mean pressure constant ¾ 0·968 ⁷⁄₁₀ 0·952 ⅔ 0·934 ⅝ 0·919 ⅗ 0·913 ½ 0·846 ⅖ 0·766 ⅜ 0·750 ⅓ 0·699 ³⁄₁₀ 0·664 ¼ 0·596 ⅕ 0·522 ⅙ 0·465 ⅐ 0·421 ⅛ 0·385 ⅑ 0·355 ⅒ 0·330 ¹⁄₁₁ 0·309 ¹⁄₁₂ 0·290 ¹⁄₁₃ 0·274 ¹⁄₁₄ 0·260 ¹⁄₁₅ 0·247 ¹⁄₁₆ 0·236 To find mean pressure:—Set 1 on C to constant on D, and under initial pressure on C read mean pressure on D. Given the absolute initial pressure, length of stroke, and admission period, to find the absolute pressure at any point in the expansion period, it being assumed that the steam expands adiabatically. (P_{2} = (P_{1})/(R^{¹⁰⁄₉}) in which P_{1} = initial pressure and P_{2} the pressure corresponding to a ratio of expansion R.) Set L.H. index of C to ratio of expansion on D, and read on the back of the slide the decimal of the logarithm. Add the characteristic, and to the number thus obtained on D set 9 on C, and read off the value found on D under the index of C. Set this number on the logarithmic scale to the index mark, in the opening on the back of the rule, and under L.H. index of C read the value of R^{¹⁰⁄₉} on D. The initial pressure divided by this value gives the corresponding pressure due to the expansion. EX.—Absolute initial pressure 120 lb. per square inch; stroke, 4 ft.; cut-off ¼. Find the respective pressures when ½ and ¾ths of the stroke have been completed.