Next Tuesday in Abu Dhabi represents Pirelli's final chance to test its prototype 2017 tyres on track before it signs off on their specification with the FIA.
As such, this final day of running will be important both for the Italian company and the sport as a whole.
The significance is that once the specification of the five compounds is set, it will remain the same from the first test of next season in Barcelona in February all the way through to the final race of the year in November.
Will Pirelli get its sums right? That's a question that can only really be answered as the next 12 months unfold.
What is clear already, however, is that it has been a huge challenge.
Pirelli has had to deal with not only the wider 2017 tyre sizes but also the massively increased loadings associated with significantly higher downforce levels. The latter has been the biggest issue, given that it's been impossible for Pirelli to replicate on-track.
It has tried, with the help of Ferrari, Mercedes and Red Bull. All three created "mule cars" based on 2015 chassis with downforce added, but without using next year's aerodynamic package, so that the teams involved would not gain any advantage over rivals.
Unfortunately for Pirelli the levels achieved didn't come close to matching what the cars will actually have in 2017, with an approximate 10 percent gain, as opposed to the 25-30 percent expected for the start of the season.
That restriction aside, it was a well-structured test programme. Up to now all three teams have had seven days of testing apiece, spread across a variety of tracks.
Each team ran all five compounds, plus the wet and intermediate. In Abu Dhabi the three mule cars will run on track together for a single day in what Pirelli calls its final validation test.
"We in general are satisfied to have these days of testing which are very important," technical boss Mario Isola told Motorsport.com.
"We always said that we need testing to develop tyres. Of course, we do a lot of designing and testing before coming on track, but track testing is really important for the final development.
"We know the effort that the three teams that are testing with us put in, developing the mule car. It was not easy. They had to start from a 2015 car modified, trying to achieve the downforce in a different way compared to the 2017 regulations.
"So it was quite difficult to do everything and to make everybody happy, because of course the other teams were worried about having a disadvantage compared to the teams that were testing.
"And it's not easy for them to develop three cars – the current car, next year's car, and the mule car, so a lot of resources were involved in that."
No representative cars
Isola admits that the disparity in downforce levels between the mule cars and the 2017 models has been a problem.
"We don't have fully representative cars, but at least we were able to test. Now the next step is to understand with the real 2017 cars what is the distance between the two, and to understand if we need any finetuning of the product.
"Of course, next year we have another 25 days, so the development is not finished. We will find for sure some areas where we need further development of our product, and we will focus our test campaign next year, when we will use 2017 cars. We will do our best to develop a new product for 2018, and so on."
Pirelli has relied heavily on data gathered from simulations run by the teams, who have revealed what they think downforce levels will be at the start of the year – and more importantly, where they will be by Abu Dhabi, after a season of development.
That information has proved to be crucial as Pirelli has extrapolated from what it has learned on track.
"It was very useful for us to have their simulations, not only for the beginning of the year, but also the end of the year.
"With this data we can tune our indoor tests to test the construction, the resistance of the construction, using the loads that they expect at the end of next year. And this is the first step of our development.
"Once we have done that, the biggest problem is to understand the performance of the compounds, by which I mean degradation, overheating, all these effects, and this is possible only with track tests.
"We are working with the teams to develop a model that is better and better, but at the moment we still need a track test to do that."
Final test key
Tuesday's final test is crucial because the deadline for finalising the specification is early December.
"We have to confirm the product and define the product to the FIA, and to send the data to the teams. So Abu Dhabi is really the last occasion on which we can confirm and validate the product for next year.
"We will have probably more than one of each to confirm, because in this case we will have three different cars running on the same circuit, at the same time, so the plan is to test the most promising solutions for next year, and to define which is the one we want to select."
One intriguing aspect of this final validation test is that the nature of the Abu Dhabi track means that it is only useful for running the three softest compounds, and thus not the hard or medium.
Pirelli's plans to test those were compromised when rain spoiled a crucial test at Barcelona in mid-October, although there was some running with Ferrari there a month earlier.
"The more difficult thing is to develop the hard and medium compounds, because unfortunately we had bad weather in Barcelona with Mercedes. Barcelona is a good track to develop hard and medium.
"Abu Dhabi is a low-severity circuit, so the hard can just slide everywhere. We tried the medium in the past, but I'm not sure it's a circuit that is stressing the medium at the right level. They just feel low grip.
"I'm confident that we can find some good soft, supersoft and ultrasoft, and then we'll see what we want to nominate. We are analysing all the data coming from previous tests to understand which are the most promising compounds in terms of hard and medium that we want to nominate.
"It is not easy because, as I said, we had some new solutions we wanted to test in Barcelona - unfortunately, it was not possible."
Of course both tyres will be run extensively in winter testing in Barcelona. It's worth noting that the medium will be used in every race from the start of the season, although the hard won't be in play until the Spanish GP in May.
So what will these new tyres be like? Will the drivers be able to push them harder for longer? In theory, yes.
"This was part of the target letter [from the F1 Strategy Group], it was a very clear request to have tyres that are not degrading, especially when they push on the tyre. It is clear and it is expected that when you follow another car, you lose grip, because you lose downforce. But once you are back in free air, you should recover this performance.
"We tested and developed new compounds, a complete new direction and new philosophy of compounds, to achieve this target, that is different to what we had to achieve in the past.
"In the past the sport was asking for degradation, to have more pitstops, to have more overtaking. Now, they're asking for something different, so we had to develop a complete new technology."
"This gave us the direction, so we understand where we have to go. Of course, we would like more and more testing, because now we have the direction, but that was the agreement.
"Of course we have to freeze the product at the beginning of the year, and then we will see with the nomination of the compounds if we have to move to harder levels or not."
That one big question remains: at the end of Tuesday's validation testing, will Pirelli be completely confident that it has got it right?
"I'm sure it is not going to happen, because you always have some doubts on your mind!," Isola concedes. "If we have to develop it for the following years, it is our job, it is something we want to do. But I am confident that we are going in the right direction."