To aid in determining a risk assessment score, a Risk Assessment Calculator that uses value ranges for five physical habitat factors can be used to establish a numerical "habitat score." In all cases, conservative physical factor ranges have been used to establish this score. This actual habitat score and the habitat score for the theoretical "perfect" zebra mussel habitat (a perfect 10, if you will) are compared to make predictions regarding an actual habitat's suitability.
To use the Risk Assessment Calculator, a user enters values for the specific physical attributes of a particular habitat. On the basis of the user-entered values, the Risk Assessment Calculator predicts the susceptibility of that particular habitat for zebra mussel population establishment. This prediction should provide a strong indication of the risk associated with a particular water body.
The Risk Assessment Calculator determines risk by calculating habitat scores that are calculated on a scale from 0 to 10. A score of 10 indicates extremely high risk of a successful invasion, while a score of 0 would represent an extremely low risk for invasion success. If a person enters one or two habitat variables as unknowns, the Risk Assessment Calculator calculates a corrected score. It does this by evaluating the habitat scores on the same scale as habitats that have data sets for all the physical variables involved. While risk predictions are strongest when there is actual physical data entered for each of the five categories, the Risk Assessment Calculator will still attempt predictions as long as at least three parameters are entered. If too little information is provided, the Risk Assessment Calculator will let the user know that additional information is needed.
The Risk Assessment Calculator recognizes the following three basic risk categories, which are based on a range of habitat scores:
The Risk Assessment Calculator can be accessed through the Risk Assessment button 
located in the information manager.