HAMMER calculates the elevation along the top of any pipe (also known as its obvert or crown) from a straight line joining the elevations of the two nodes it connects to. Because differences can occur between as-constructed pipe elevations (or surveys) and the design drawings that hydraulic models are typically based on, it is prudent to assess the sensitivity of the hydraulic transient simulation results to changes in elevation. If the transient HGL drops below the pipe elevation, vapor pockets can form and collapse.

HAMMER speeds this process by allowing you to make a global adjustment to pipe elevations from the Tools > Options menu command; click the Preferences tab and type in the amount to increase the pipe elevations. After running HAMMER, you can save the resulting profile as a HAMMER graph (.grp) and copy data from several such graphs onto a common graph showing the sensitivity to elevation errors.