Sounds like you have numbers stored in a field of type text. Text is ordered by the rules needed to sort text into alphabetic order rather than the numeric order you'd get for numbers in a number field. (this is a fairly common mistake that I've made myself from time to time.) Also keep in mind that calculation fields specify a result type that can be either number or text.
The following numbers are arranged in ascending order if the numbers are in a text field rather than number. Logical value comparisons such as inequalities also use the same rules.
Ah, that sounds incredibly likely. Is there anyway to change a text field to a number field, that doesn't involve creating a new number field, and copying and pasting each result?
Open Manage | database | Fields
Find and click the field to highlight it. The field's name and data type will appear at the bottom of this window. Just change the field type from "text" to "number". If this is a calculation field, you'll need to open up the calculation and select the "number" result type from a drop down.
Sorry for the late reply - this worked perfectly. Many thanks!