the space consumed. Such low rise stairs were built into the Winchester Mystery House to accommodate the infirmities of the owner, Sarah Winchester , before the invention of the elevator . These stairways, called "Easy Risers" consist of five flights wrapped into a multi-turn arrangement with a total width equal to more than four times the individual flight width and a depth roughly equal to one flight's run plus this width. The flights have varying numbers of steps. Slope: A value for the rise-to-tread ratio of 17/29 ˜ 0.59 is considered optimal; [ 3 ] this corresponds to a pitch angle of about 30°. Variance on riser height and tread depth between steps on the same flight should be very low. Building codes require variances no larger than 0.1875 inches (4.76 mm) between depth of adjacent treads or the height of adjacent risers; within a flight, the tolerance between the largest and smallest riser or between the largest and smallest tread can not exceed 0.375 inches (9.5 mm). [ 10 ] The reason is that on a continuous flight of stairs, people get used to a regular step and may trip if there is a step that is different, especially at night. The general rule is that all steps on the same flight must be identical. Hence, stairs are typically custom made to fit the particular floor to floor height and horizontal space available. Special care must be taken on the first and last risers. Stairs must be supported directly