Mismatch due to ageing

[MicheleANE]

Hello,

Please see the figures below:

 

 

Around the 10 years zone, there is a sudden change in the curve and also the values for the mismatch due to ageing. After that, the curve goes back to mostly linear like before the 10 years zone.

We found this behavior in several cases and we don't understand why it's so.

We would expect the mismatch to keep growing more and more, maybe fluctuating around a more exponential curve because of the randomness of the calculations.

Can we have an explanation of this happening?

Best regards

Michele