So what is the format of the column? Test/string I imagine?
It is generally a very bad idea to have a column of mixed values (strings/numbers).
In order to get the maximum/minimum numeric value, you are first going to need to convert the values to a number. The following formula will convert all numbers to that numbers, and all text to 0:
Code:
ConvertField: IIf(IsNumeric([MyField]),[MyField]+0,0)
where MyField is the name of your field.
You can place criteria on this field to remove the the zero entries (note that if you may have 0 numeric entries that you want to include, we will need to get a little more creative to just remove the ones that come from the Text values (by using the IsNumeric field in a separate calculation).
You can then use the Maximum/Minimum Aggregate Function on this calculated field we show above.