"When we're truly testing, we have a lot more sensors on the car and a lot more data," explains Harris. "A lot of the time that's trying to correlate between other systems - our wind tunnel or CFD [Computational Fluid Dynamics] in our computerised simulations.
"When we're racing it's not all about reliability. There is performance-related data in there as well, and we're always trying to be able to make the right decisions as quick as humanly possible."
They use multiple data sources to assess performance but one stands out above the others.
"If you were to ask anybody that's in F1 that knows what they're talking about, the biggest possible differentiator between any of the teams at the moment is tyres," says Harris.
"Now you'll hear lots of people going on about the engine - and yes, that's important, and we're lucky enough to have one of the best in the pit lane - but if we get tyres wrong we won't be the fastest. We could quite easily be mid-table."
Simulations of the car and analysis of sensor data help them optimise tyre performance and get the fronts and rears to work together at the right temperature.
Tyre degradation also plays a critical role in pit stop strategy.
Multiple streams of data help the team sat in the control at the pit wall decide what to do. Some of it is based on what they understand about tyres, and some of it is based on what is happening live on the circuit. This could be different to the data from the previous day's practice or qualifying laps due to changing conditions such as track temperature, rain, or crashes.
The team will also assess the decisions made by their rival teams and the effect that they have on performance.
"Generally we'll know what we think we should be doing via simulation, but the human element always comes in there," says Harris.
Those simulations have nonetheless becoming increasingly vital in his 20 years in the sport, particularly due to a spate of recent restrictions on testing.
"I'd say simulation's probably the biggest technology change. All the physical things that got taken away by rules we've tried to do in computer simulation. We've gotten more kit simulating what we should be doing at an event, how the car should be set up, how the car should run."
Mercedes has always been very data-driven at the track, and is trying to extend this approach throughout the organisation.
"We've always been incredibly data-driven in everything we do at the track," says Harris. "Even if the driver turns around and tells you that something happened at a certain part on the track, we will always go back to data to prove why and where and how it happened, and what we should do and how we should change it.
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