Each variable used by an algebraic question must be specifically entered in the question configuration. This is to ensure correct handling by the comparison algorithms. All question answers are checked for variables and an error will be flagged if a variable is found in a question which has not been declared.
There is a maximum and a minimum value for each variable. This need only be filled in if the Evaluation comparison algorithm is used. It can be specified for the other algorithms but will be ignored. These values define the range over which values will be randomly chosen. Care should be taken to ensure that the question answers are well behaved over this range.
For example if one of the question answers is '1/x' the range for the variable 'x' should not include zero! Also be aware of variable interactions may also cause problems. For example if you have an answer '1/(x-y)' you must ensure that the ranges for x and y are such that they do not overlap which may give x=y. Similary when using inverse sine or cosine you must ensure that the argument never exceeds 1. Note that in the case of a mistake the program will not crash but comparisons may well be inaccurate.