Pen accuracy/dosing help?

[mercuryleaf7]

Would someone be able to help me/explain what's going on here?

So I got some V1 pens and I decided to test the accuracy where you stick an insulin syringe into the pen, dial up the units, press the plunger then check the reading on the syringe to make sure its the same as what you intended.
However I've noticed something really strange, whenever I do this for the first time it keeps underdosing yet whenever I do it for subsequent tries even as low as 2 units its dead on accurate.

This is what I did:
1. Insert cartridge into pen.
2. Add pen needle and keep dialling up the pen until the plunger is in contact with the cartridge stopper and some liquid comes out.
3. I then set it to 2 units, flicked it similar to a Mounjaro pen to ensure there's no air bubbled and pressed the plunger and the 2 units shot out so we can assume everything is accurately setup now and it should be ready for a dose?
4. Remove pen needle and insert insulin syringe.
5. Dial to any number of units 20, 60, 80, hold syringe and pen steady and press plunger. It underdoses
6. Remove insulin syringe, squirt out liquid, put it back in the pen and try the 20 units again. Dead on accurate.
7. Get rid of liquid try 2 units, 5 units, 10 units, 20 units etc. All dead on accurate.

It's as if the first dose you would take is always going to be inaccurate and this has been the same on all 4 pens I've tested and I don't understand why as I've taken all the correct steps to begin with to eliminate air and ensure the plunger is in proper contact with the cartridge stopper.

 

[IshimaruKenta]

Are all your pens V1 models or do you have any name brand ones? Not blaming the V1/V2 but I'm sure they don't have the same manufacturing tolerances that a name brand model would have. I have yet to test my pens for accuracy as I really don't like the idea of having to waste a cart just to find out. Maybe I should buy some from AliExpress and use those to test. 🤔

 

[mercuryleaf7]

Are all your pens V1 models or do you have any name brand ones? Not blaming the V1/V2 but I'm sure they don't have the same manufacturing tolerances that a name brand model would have. I have yet to test my pens for accuracy as I really don't like the idea of having to waste a cart just to find out. Maybe I should buy some from AliExpress and use those to test. 🤔

I've got 4 V1 pens off Alibaba and a Lilly Luxura.
The Luxura seemed sporadic with its dosing which is why I've bought these.

I don't understand why the dosing is only inaccurate the first time the pen is used, I am using insulin syringes/needles (so the needle is fixed, extremely low dead space) and I know the issue isn't with that or it wouldn't be displaying the correct amount of units the following times.

And I took all the steps before hand to ensure there was no air etc.

 

[miss-sanne]

Would someone be able to help me/explain what's going on here?

So I got some V1 pens and I decided to test the accuracy where you stick an insulin syringe into the pen, dial up the units, press the plunger then check the reading on the syringe to make sure its the same as what you intended.
However I've noticed something really strange, whenever I do this for the first time it keeps underdosing yet whenever I do it for subsequent tries even as low as 2 units its dead on accurate.

This is what I did:
1. Insert cartridge into pen.
2. Add pen needle and keep dialling up the pen until the plunger is in contact with the cartridge stopper and some liquid comes out.
3. I then set it to 2 units, flicked it similar to a Mounjaro pen to ensure there's no air bubbled and pressed the plunger and the 2 units shot out so we can assume everything is accurately setup now and it should be ready for a dose?
4. Remove pen needle and insert insulin syringe.
5. Dial to 20 units, hold syringe and pen steady and press plunger. Underdoses at around 15-17 units.
6. Remove insulin syringe, squirt out liquid, put it back in the pen and try the 20 units again. Dead on accurate.
7. Get rid of liquid try 2 units, 5 units, 10 units, 20 units etc. All dead on accurate.

It's as if the first dose you would take is always going to be inaccurate and this has been the same on all 4 pens I've tested and I don't understand why as I've taken all the correct steps to begin with to eliminate air and ensure the plunger is in proper contact with the cartridge stopper.

hmm that's strange. is it brand pen ?

 

[mercuryleaf7]

hmm that's strange. is it brand ?
sounds like you do it very correctly

Just a generic pen off alibaba.

So the only conclusion I am coming to here maybe is that the travel of the plunger for a certain distance is inaccurate but once it gets past that it is accurate?

Very strange behaviour cause you'd expect it to be inaccurate later on too!

 

[miss-sanne]

Could be, don't know.
I have the original Eli Lilly huma savvio pens, and it did do something like that a few times, not in the beginning of cartridge though. I never found out why, I could just see the plunger not move. (it was a large dosis)

 

[mercuryleaf7]

Update!
I've tested all 4 V1s and a Lilly Luxura, using both an official Lilly cartridge and an AliExpress cartridge had myself and a friend try it to try and isolate if its me or not and same issue with underdosing on the first dose.

Very weird.

 

[miss-sanne]

Update!
I've tested all 4 V1s and a Lilly Luxura, using both an official Lilly cartridge and an AliExpress cartridge had myself and a friend try it to try and isolate if its me or not and same issue with underdosing on the first dose.

Very weird.

that is a mystery ! just discard first dose then ?

 

[mercuryleaf7]

that is a mystery ! just discard first dose then ?

I could do but I think I'm onto something here that other people haven't realised.

But I'm thinking surely this is happening to everyone and they haven't realised.
Seems very suspicious it is happening when 2 separate people are doing the test, cartridges from 2 different origins, 2 completely different pen manufacturers.
All those possible ways to eliminate an error and its consistently happening.