Mercedes boss Toto Wolff admitted his team "got the math wrong" in making the pit call that cost Lewis Hamilton victory at the Monaco Grand Prix.
The pit stop was made on lap 66 under a safety car and dropped Hamilton from the lead to third place. Wolff said the decision was made in an attempt to pre-empt a similar strategy being used by Ferrari's Sebastian Vettel in third, but the team based the call on incorrect information that told them Hamilton would resume in the lead.
"What the hell happened there, that is exactly the right question," Wolff said. "The simple answer is we got the math wrong, the calculation wrong. We thought we had a gap which we didn't have when the safety car came out and Lewis was behind the safety car. The calculation was simply wrong and that's what happened."
The teams usually base such decisions on GPS data from the cars, but the tall buildings of Monte Carlo means the data is not available in Monaco. Added to the confusion caused by race control's decision to initially deploy a virtual safety car (a method for neutralising the race at a lower speed) before releasing the actual safety car, Wolff said the team got its decision wrong.
"In Monaco you have no GPS and that makes the whole exercise more difficult and this is why we got it wrong when it switched from virtual safety car into safety car.
"The final decision was made 50 metres before the pit entry."
Pushed on why the team considered risking a pit stop when track position is key at Monaco, Wolff said: "The potential risk could have been that Sebastian would switch on to a soft tyre behind us and coming up behind Nico, it could have been a risk at the end. Now, let's say, very simply from a common sense overview disregarding the data ... we have to follow the data. This is how the squad works, but I agree it looks like a risk. The simple answer is that the numbers were wrong."
Wolff said it was a joint decision between team and driver.
"The decision is being made jointly with a lot of information at the same time but in a fraction of seconds you need to make a call. We tried to make as much input as possible from the engineers, from the management and from the driver and then you take a decision. In that case the algorithm was wrong."