Crossed Cylinders makes adding cylindrical lenses easy.
When two cylindrical lenses of arbitrary orientation are placed in series, the resulting combination is equivalent to a lens with both spherical and cylindrical power. The computation of the equivalent lens power is non-trivial and care must be taken to make sure that the results are correct. The Crossed Cylinders application makes this computation easy, and has the added feature of allowing each lens to have both spherical and cylindrical power.
Using Crossed Cylinders is simple. Spherical power, cylindrical power (in diopters) and the axis angle of each lens is entered using either sliders or the keyboard. As the values are entered, Crossed Cylinders displays the combined power of the resultant equivalent lens using both the + cylinder and - cylinder conventions. Crossed Cylinders also has the option of rounding the results to the nearest 1/4 diopter.