Digital Teaching Stamp Roller】Adjustable numbers, gently rolling, can efficiently and quickly print out math practice questions within 100, it is a fun and meaningful gift for your children or friends’ children!Each stamp has a side gear that you can turn to generate up to 100 different equations for each operation. So that makes 100 different equations for each operation. How do I refill the stamp? Just pop off the lid on the side, pour in the ink, and you’re good to go!