When SCS equation is used to calculate the rainfall excess in pervious area, the Curve Number (CN) is the most important parameter. From the early research of OTTHYMO, it has been rec-ommended to use the modified CN, i.e. CN*. VO has provided a tool (Convert to ) to convert the CNII to CN*. To indicate the conversion has been conducted, a check box is given on the right of the CN property as shown in the figure below. The sole purpose of this check box is to tell the CNII has been converted to CN* to avoid repeating the conversion. It’s not recommended to manually uncheck or check it although it doesn’t affect the CN value.