# Volume of insulin left in pods as calculated by Loop?

**URL:** https://forum.fudiabetes.org/t/volume-of-insulin-left-in-pods-as-calculated-by-loop/11035
**Category:** Pump
**Created:** [March 9, 2021, 3:04pm UTC](https://forum.fudiabetes.org/t/volume-of-insulin-left-in-pods-as-calculated-by-loop/11035 "2021-03-09T15:04:42Z")
**Posts on this page:** 1
**Showing post:** 3

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### Author: ![Eric](https://yyz2.discourse-cdn.com/flex030/user_avatar/forum.fudiabetes.org/eric/32/9209_2.png) [@Eric](https://forum.fudiabetes.org/u/Eric)
#### Post date: [March 9, 2021, 4:48pm UTC](https://forum.fudiabetes.org/t/volume-of-insulin-left-in-pods-as-calculated-by-loop/11035/3 "2021-03-09T16:48:47Z")

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@TiaG,  
Let me shock you. The OmniPod - both pod and controller - actually have **NO** idea how much insulin you put in it when you start! It only knows - did it go past the minimum fill mark? And that is based on the plunger inside moving past a certain point.

And then after that, it still has no idea how much insulin is in the pod… **UNTIL** the plunger gets to the 50 unit mark. Again, based on plunger position. So that 50 unit mark is just another **rough** estimate. And that rough estimate is always going to be under-estimated.

The pod sends a signal saying it is at the 50 unit mark - and from there, the controller (either the PDM or the phone in your case) does the math.

The other thing is that the number of units remaining has a built in safety, like a car’s reserve tank. There is **always** a little more insulin in the pod than what it says. There is no way Insulet could get away with a pod saying it had 7 units, and it actually only had 2 units. They would get fried by customers and the FDA if they did that.

So when it says 10 units, you really have a little more.

> [@TiaG](#):
>
> Currently Loop says just 16.4 units remain. My rough calculations suggest there should be at least 10 units more in the pod.

Just like when your car tank says it is empty, there is enough gas to get you to the grocery store, stop off at the dry-cleaners, and then drive to the gas station. Just because that is human nature.

Here is some FUD discussion on the reserve tank:

> [@The OmniPod's "reserve tank"](https://forum.fudiabetes.org/t/the-omnipods-reserve-tank/1957):
>
> I have been tracking this down for a while. Finally got a somewhat official answer, which matches the tests and numbers I came up with on it. If you are a OmniPod user, the conclusion may possibly be of use to you at some point. The OmniPod PDM shows units remaining. But is it never exactly correct. I always noticed a bit more insulin in the pod than what is actually displayed on the PDM. But the “how much” was somewhat of a mystery. So I started loading my pods with very specific amounts wit…

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