By default, the 'Number' field accepts all numbers. But you might want to:

• Accept only positive numbers.
  
• Reject numbers over, say, 1000.
• Accept only whole numbers. (Reject 0.50, 100.01 etc.)
  
• Accept only those numbers that are a multiple of, say, 5.
  

Particularly, if you'd only like to accept 0, 5, 10, 15, .... 1000, do the following:

1. Add (or edit) a field of type 'Number' and check 'Show more configuration'.
2. Against 'Min. Value', 'Max. Value' and 'Step Size' enter 0, 1000 and 5 respectively.
3. Click Done.
   

Now, try using the up-down arrow keys next to the field-preview. You'll see that the numbers in the field-preview will follow the pattern: 0, 5, 10, 15, .... 1000. The number won't fall below zero and won't exceed 1000.

Each of these is optional:

Please note that each of 'Min. Value', 'Max. Value' and 'Step Size' is optional. You may use all of them, none of them, two of them, or just one of them. It's all up to you.