D-13 
Figure D-14. Math screen with files chosen to "Derive New Parameter" 
of Dissolved Oxygen by subtracting File 2 from File 1 to create the 
output file. 
the mean for the five files. Another example would be to subtract interpolated 
dissolved oxygen data from an interpolated saturated dissolved oxygen file to 
compute the oxygen deficit. 
The code checks whether the input files have the same number of segments. If the 
input files (“Input .est File 1” and “Input .est File 2”) do not have the same number 
of segments, they were generated from different bathymetry files, and the cell values 
in the two files can not be properly combined. An error message will be displayed if 
this condition occurs. 
The “Recode Parameter Value” radio button provides the means to convert calculated 
values to new values (Figure D-15). The input file is not changed, but a new output 
file is created with new values in each cell which classify the data into new values 
or categories. For example, to compute the interaction of dissolved oxygen and water 
temperature: 
1) Recode the dissolved oxygen .est file so that oxygen below 3 mg/1 is set to “1” 
and oxygen above 3 is set to “0” (also set missing to -9). 
2) Recode the water temperature .est file so that temperature below 25C is set to “0” 
and temperature above 25C is set to “10” (also set missing to -9). 
3) Derive a new parameter “WD” by adding the recoded dissolved oxygen and water 
temperature .est files. The result is a wd.est file where: “0”=acceptable oxygen and 
temperature; “l”=unacceptable oxygen; “10”=unacceptable temperature; and “11”= 
unacceptable oxygen and unacceptable temperature (missing cells will = -9). This 
file can be graphed to show the distribution of these categories. The water column 
appendix d 
User Guide and Documentation for the Chesapeake Bay Interpolator 
