The Fill Median Ranks feature is available only for data sheets that have been configured to support free-form data. It enables you to obtain the median ranks for a given set of failure times, allowing you to experiment with the unreliability estimates for each failure and see how they affect the solution of an analysis.
To generate median ranks, enter the times-to-failure data in the "X-Axis value" column of the data sheet, then choose Life Data > Options > Fill Median Ranks.
For each time-to-failure value in the "X-Axis value" column, the "Y-Axis value" column is filled with the corresponding median ranks value. On the control panel, choose a distribution and then choose Life Data > Analysis > Calculate or click the icon on the Main page of the control panel.
The software will compute the parameters of the distribution based on the data set. You can use the plots and the QCP to obtain results based on the calculated parameters; however, calculations involving confidence bounds are not available.
The ReliaWiki resource portal has more information on median ranks at: http://www.reliawiki.org/index.php/Parameter Estimation.