There will be just three days of preseason testing before the opening race weekend of the 2023 Formula One season, and they are about to get underway Thursday through Saturday.

The number of test days has been halved this year due to stability in the regulations from last year, and all three days will be held at the same Bahrain International Circuit that hosts the first race on March 5.

F1 testing always generates excitement among fans as the drivers get back on track, but the timesheets at the end of each day can be misleading. Below is a guide to what testing is all about and how much you should read into the headline lap times from the upcoming track action.

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F1 cars are meticulous pieces of engineering, but at this time of the year they also represent 200 mph science experiments. While a great deal of work goes into making a new F1 car go fast over the winter, there's still the potential that the wheels come off (sometimes literally) when the it leaves the garage for the first time.

As a result, F1 teams go through rigorous debugging and refining processes with their cars before the first race to make sure they are as fast and reliable as possible when the lights go out at the first race. In the past this process was often spread over more than 10 days of preseason testing, but to save costs, the number of test days has now been reduced to three.

The opening morning of testing is usually spent running system checks on the car to make sure everything is operating as it should. Although teams have advanced test benches at their factories and will likely have completed a 100km shakedown prior to Bahrain, nothing compares to running the car all day in the heat of Bahrain's desert sun.

Checks of the hydraulic system, electrical system and cooling systems are crucial early on the first day to flush out any potential reliability issues. In race specification an F1 car carries over 300 sensors to ensure its extreme tolerances are not breached, but in testing that number is much higher so as to harvest as much real-world data as possible.

Sensors are sometimes too small to spot or exist under the bodywork, but when it comes to understanding a car's aerodynamics they are usually impossible to miss. Big metal fences known as rakes are attached to the cars behind sensitive areas of airflow to measure air pressure and understand how the flow structures around the car.

The rakes are made up of a series of "pitot tubes," and their readings are compared with the work the teams have conducted over the winter in the wind tunnel and via CFD (computational fluid dynamics). If the real world data matches up with the simulations, a team is already several steps closer to extracting the true potential of the car at the first race. If they don't, the team is already on the back foot.

Feedback from the driver is also key. Simple things such as the seating position often need to be adjusted, and long days in the cockpit are the best way to find out what's comfortable and what's not. Steering feedback and brake feel are also early boxes to tick, although it can take over half a season before a driver is truly happy with the finer details. More experienced drivers can also help engineers understand where lap time is leaking away by describing the behavior of the car through the corners.

Once it's been established that the fundamentals of the car are operating as they should, teams turn their attention to its setup. Finding the right car setup is crucial to unlocking performance and knowing how a car will react to different ride heights, wing angles and suspension settings helps engineers build up a toolbox of solutions as they better understand the car.

Engineers will spend large parts of testing working through different setup combinations to find out what works and what doesn't across different fuel loads and tyre compounds. Gaining as much knowledge as possible at this stage of the year can pay dividends later on in the season when handling issues appear in the heat of competition.

A reliable car that responds well to set-up changes is the aim by the final day of preseason, along with reams of data to inform the next steps of car development.

After the complete overhaul of Formula One's technical regulations for 2022, the changes this season are relatively minor.

Tweaks have been made to the regulations around the floor of the cars -- raising the edges by 15mm and introducing more stringent flexibility tests -- to reduce their sensitivity and decrease the propensity for "porpoising," which plagued much of the grid at the start of last year. The FIA will continue to monitor the car's oscillations on track and disqualify any car that is bouncing with a level of violence deemed dangerous to the driver.

Crudely applied to last year's cars, the rule change would cost at least half a second per lap, but the main aim of the teams over the winter has been to claim that lap time back and uncover more performance. It was thought the rule change, which became a political issue between teams during 2022, might favour teams that struggled with porpoising last year, such as Mercedes, but it remains to be seen if it has any impact on the competitive order.

Smaller changes to the technical regulations include larger wing mirrors to improve the driver's visibility, tougher crash tests for roll hoops and a reduction in the car's minimum weight by 2kg.

The lap times as they appear on the timing screens during testing are rarely an accurate picture of the competitive order. However, it is possible to start to build a picture of who's quick and who's not by digging a bit deeper into the data and keeping an open ear to what's being said to the media.

One clear sign that a team is struggling is a lack of mileage. While that will usually indicate an obvious reliability issue, it also means the team is not progressing with the performance of the car simply because it is not getting the track time or data to move forward.

Assuming the car is reliable, the vibe around a team during testing can also indicate where it stands. Engineers and drivers are always keen to play down expectations at this time of year, but in the close-knit F1 paddock, confidence levels become increasingly easy to gauge after a couple of days on track.

But the mystery surrounding testing doesn't mean you should completely disregard lap times. By looking out for certain patterns, it's possible to gain some understanding from the data popping up on the official timing screens. Away from aero and systems testing, the lap times can be split into two types of data -- both useful for building an understanding in their own way.

These are the laps run on a relatively low fuel load with the aim of better understanding the car's true performance over a single lap. They are easy to spot as the drivers will alternate between "hot laps" and "cool-down laps," creating a tell-tale pattern of fast, slow, fast, slow on the timing screens.

Drivers have to intersperse their fast laps with slower ones to allow the tyres to recover after being pushed hard on the previous lap and to recharge the battery in the car's hybrid system, which will use up all of its power on a qualifying-style lap.

Tyre compounds are key to one-lap performance and Pirelli offers all six of its compounds to the teams during testing. The compounds are numbered C0, C1, C2, C3, C4 and C5, with the newly-named C0 being the hardest and the C5 being the softest. The C0 is actually the same compound as last year's C1, while this year's C1 is a new compound to fill the gap between C0 and C2.

Softer rubber provides more performance but is less durable, meaning the softest compound may only be good for a single lap before it loses its peak performance. The fastest times are likely to be set on the softest tyres in testing, but if a car using C2s is only 0.1s slower than a car on C5s, it's safe to assume the car on the harder compound has a significant underlying pace advantage.

Temperatures can also fluctuate throughout the day, with Bahrain offering its optimum track conditions once the sun has set and the tarmac has cooled. As a result, a time set on C5s in the heat of the midday sun is not comparable with a time set on the same compound under the floodlights late in the day.

These are all factors that need to be taken into account when looking at the fastest laps each day, but even if you know the tyre compound and the time of day at which the lap was set -- which are both public information -- you still only know half the story.

A car's fuel load is a major factor in performance and 10kg can add roughly 0.3s of lap time. Put another way, a car with a full tank at the Bahrain International Circuit will be over 3.5s per lap slower than a car running on fumes. The reality is that most of the time the teams will run a fuel load somewhere in between, as the extra weight of running on a full tank will damage the tyres after a handful of laps and running on qualifying amounts of fuel will mean the car will have to return to the pits more often to refuel.

There is no way of knowing how much fuel a car has on board from the outside and teams are not obliged to hand out figures. As a result, the most impressive lap time in testing might be set by a team running with 40kg of fuel in the tank, while a fundamentally slower car can look surprisingly competitive by running 20kg or less. Loading the car with fuel during testing is often referred to as "sandbagging" -- F1-speak for a team hiding its performance -- but the truth is that a fuel load between 60kg and 30kg offers a more practical baseline for understanding car performance.

Unfortunately, the most useful tool to cut through the secrecy and make sense of lap times isn't available to fans and the media. Teams closely monitor GPS traces of rival cars to gather data on both corner speeds and straight-line speed, allowing them to build a clearer picture of true car performance. The speed at which a car accelerates and brakes is useful to guesstimate both its engine mode and fuel load, and at the click of a mouse that data can be cross-referenced with previous years' test sessions or races to identify trends and spot anomalies.

What's more, F1 teams are creatures of habit and will often stick with a set fuel load for testing from one year to the next. As staff move from team to team over seasons, it doesn't take long for an experienced engineer to build up a bank of data and knowledge to help sift through the times popping up on the timing screens and pick out the true star performers.

One way of removing the uncertainty over fuel loads is to look for teams attempting "race simulations." In an ideal world, most teams will aim to complete a race simulation by the end of testing so that they can gain an understanding of how the car performs over a grand prix distance and gather data that could increase their points haul a week later at the same circuit.

In order to complete a race distance without returning to the garage to refuel, cars will need to leave the pits at the start of the run with close to the maximum fuel load of 110kg. And once we know cars are starting out with the same fuel load to complete the same number of laps, it makes it much easier to compare performance.

It's not an exact science as the time of day, track conditions, engine modes and tyre strategies can skew the results, but as a general rule it is the best way to build a more accurate picture of performance by removing some of the questions over fuel load. Race sims can easily be spotted by a series of slow but steady lap times over long runs that are interspersed by race-style pit stops, where the pit crew will practice tyre changes as they would do in a real race. Alternatively, if you spot that a driver's pit board is counting down from 57 laps (the length of a grand prix in Bahrain) the chances are they are attempting a race sim.

By working out an average lap time from each driver's race sim it's possible to get the best indication of how quick a car really is compared to its rivals. However, because race sims are usually among the last tasks on a team's job list, it's possible they simply won't be able to fit them in over this year's shortened three-day schedule. If that's the case, it will be back to guesstimating fuel loads in an attempt to compare cars like for like.

While some kind of order usually emerges from testing, it's not always representative of the first race. This year the sole preseason test and the first race are being held at the same venue, in Bahrain, improving the chances of an accurate prediction. But even so, a lot can change in a week. ..

Teams always hope to develop rapidly at the start of a new season as they gain an on-track understanding of their cars to compare with simulation data. A car that starts slowly might be a few setup changes away from unlocking significantly more pace, but the key to that performance might only present itself after the data has been fully analysed at the end of testing. Based on the data gathered over the three days, teams will also be able to refine their setups in the driver-in-loop simulators back at their factories.

What's more, the cars that run in testing this week may look surprisingly basic or underdeveloped when we look back at them at the end of the year. For the bigger teams some updates will come as early as the first race and its not unusual for performance to be unlocked by an upgrade between testing and the season opener.

With the exception of passing crash tests prior to running and obeying marshal flags, there are very few rules governing testing. Running is unlimited between 9 a.m. and 6 p.m., although tyre allocations put a practical limit on how many laps can be completed over the three days.

There is no scrutineering and teams could, in theory, test parts that are illegal under the regulations as long as they come off again for the first race. In 2013, Caterham and Williams ran small bits of bodywork to divert exhaust gasses towards the car's diffuser, which would have been illegal under the regulations but allowed them to gain a better understanding of how other teams were benefiting from doing exactly that within the regulations.

In 2020, Mercedes caused a stir by trialing its innovative but controversial dual axis steering (DAS) system during preseason. It was a device the FIA was aware of and had already moved to outlaw for 2021, but was technically still legal under the 2020 regulations.

After studying its use throughout testing, rivals Red Bull protested DAS at the first race of the season in the hope of proving it was illegal (or perhaps just finding out more information about how it worked) leading to an official ruling from the FIA that it was indeed legal.

Testing is the first chance teams get to see what their rivals have built for the new season, so questions of legality are often raised, even if it's just behind closed doors or via leaks to the media.