Aha, yes, its complex. here goes:
Inertia means that the actual value that is looked at is ‘x’ turns old. So if we are the effect of police force policy reducing crime, and inertia was 4, that means that the actual effect on crime is 4 turns out of date. So if I raise police spending, it will take 4 turns to see the effect. if I cut spending, it will take 4 turns for that to filter through. This can vary from effect to effect within the same policy.
Implementation is different.
If something takes 10 turns to implement, then it gradually ‘fades in’ over those 10 turns. So at the end of turn 1, it is 10% done and having 10% of the effect. This also means that changes to the policy can take ‘up to’ 10 turns to happen. So if the policy is at zero and you move the slider to maximum, this will slowly happen over 10 turns. if its a minor adjustment, its obviously quicker. This is totally different from inertia. Only policies have implementation time, but all kinds of effects can have inertia.
The best way to look at it is like this:
Say it takes 10 turns to implement a new police force. This is the time it takes to recruit new police, train them and get them on the streets. There will be some police on the streets sooner than this, and gradually the entire force will be recruited. it takes 4 turns for this new police presence to actually filter through to the criminals enough that they go and get proper jobs. (but this will seem to fade in too, because the number of police is fading in over time).
So in total, the full effect will take 14 turns to happen, although other effects within the same policy (with different inertias) will respond differently.
I guess it is a bit confusing, but it’s trying to model different stuff. Implementation delays are there so that policies with a lot of infrastructure (like laying new railway track) take time to put in place. inertia is there so we can model effects that are very gradual (it takes a while for any measures that raise literacy to take effect, because people are at school for a long time etc).
Does that make sense?