Some pumps also allow you to take multiple doses of insulin in short periods of time because it can mathematically, according to how well it is programed, know approximately how much insulin is still in your body and subtract this amount out of any future amount of insulin that will be delivered via the pump for meals, snacks or high blood sugars. The pump has the user enter in a time frame, usually in hours for approximately how long it takes a person to break down or use up the insulin once it is delivered into the body. This function is typically called Insulin-on-Board. If a person has this function set for three hours, they are saying that once insulin is delivered into their tissue, it takes three hours for their body to metabolize the insulin so it is completely broken down and after three hours, the insulin would have no effect on the person’s blood sugar level.
This function is very useful and helps the pump know when it may need to subtract insulin from a determined dose because there is still ‘active’ insulin in the person’s body. An example when this function works is when a person eats dinner, and gives their dose of insulin for the meal, but an hour later, would like to have a dessert. The pump then, will calculate approximately how much "active" insulin is still in use and will subtract out this amount from the dose of insulin needed for the dessert they are planning to eat. This helps a person avoid low blood sugars when giving insulin within short periods of time for eating or for correcting high blood sugars.