Dynamic classification model for company sales

Hi, 

we want to make a dynamic company sales. The companies should be divided into different groups due to their sales amount. I have written down the model: 

The user should be able to select a stepsize (or number of classes) and all the classes and their companies should be updated automatically. In this case the difference between max and min is 99 and the user chooses a stepsize of 9. Therefore there should be 10 classes of the stepsize 9. If the user chooses stepsize 99, there should be only 1 class with all the companies in it.

Does somebody have any idea how to do this? In addition, one would have to be careful if the stepsize is not divisible as a whole number by the difference but has a remainder. In this case you would have to round up or similar.