PROGRESSION is rarely linear.

Carlton is finding that out the hard way this season, with the club's rebuild brought into question once again after a disastrous first-half performance at home to Fremantle last Saturday saw Brendon Bolton's side slump to 1-11, with a meagre percentage of just 61.9.

While the Blues set about starting fresh with a 'Year Zero' approach almost three years ago, the reality is the building blocks for their long-term future are still being put in place.

Internally, Bolton is not a man under pressure. Not much will make that change in 2018.

But over the next two years, the Blues will need to show tangible improvement in order to prove this 'reset' is on track. And while the club won't necessarily need to show that it's a contender again in that time, supporters should know exactly where it's heading by 2020.

With that vision in mind, here are the three key questions currently facing Carlton's rebuild.

Where is Carlton at?

Melbourne has perhaps provided rebuilding clubs with a blueprint for how to do things.

Over five years, since the club's disastrous 2-20 season in 2013, the Demons have shown linear progression under the reign of both Paul Roos and Simon Goodwin.

The club's win total each year has steadily risen from four in 2014 to 12 last year, with Goodwin's men set to eclipse that mark and challenge for the top four this season.

Carlton, in essence, is three years into that five-year process. However, the Demons did start from a much younger base than the Blues.

Melbourne was the fifth-youngest side in the competition in Roos' first year in charge, whereas the Blues were the seventh-oldest in Bolton's maiden campaign. It's meant Carlton has made 42 list changes in the three years since, compared to Melbourne's 47 in five.

The quality that has left the list further emphasises Carlton's starting point. Of the 42 players that have departed since Bolton took charge, just seven remain on an AFL list.

The club has also been forced to lose A-Graders in order to replenish its draft stocks, with Bryce Gibbs, Zach Tuohy and Lachie Henderson leaving over the last three years.

Bryce Gibbs played 231 games across 11 seasons for the Blues. Picture: AFL Photos

However, the Blues must now start to regain some much-needed experience. Just as the Demons' age profile has subsequently lifted over the last two years, the Blues' must as well.

The club has made no secret of its desire to target an experienced player between the age of 22 to 26 at season's end, so expect that age demographic to begin to lift.

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Carlton currently has 12 players in that age bracket, which generally coincides with when most footballers hit their peak. Compare that to Melbourne, who has exactly double that number this season, and perhaps it's no surprise the Blues are struggling. 

What do the Blues still need?

Carlton needs experience. It's why the club is keen to retain skipper Marc Murphy.

While Melbourne got significantly younger throughout its rebuild, the Demons also targeted experienced heads to guide the kids, and recruited Bernie Vince and Jordan Lewis to do that.

Murphy could provide that type of senior experience. But he needs help, which is why the Blues will also focus on free agents and trade targets at season's end.

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Andrew Gaff and Rory Sloane are clearly names that will be in the mix for Carlton.

Should the Blues be able to attract such prospects, they will give Patrick Cripps much-needed midfield support and will help the development of young onballers like Sam Petrevski-Seton, Paddy Dow, Zac Fisher and Lochie O'Brien.

Patrick Cripps has shouldered an unhealthy load for the Blues. Picture: AFL Photos

But having laid the foundations for its rebuild primarily at the draft, Carlton also desperately requires depth players that can provide both an example and a buffer for its youngsters.

The club's current middle tier is an area worthy of significant attention. The likes of Jed Lamb, Sam Kerridge, Aaron Mullett and Cameron O'Shea, among others, perhaps won't be part of the club's long-term future. The Blues simply must find players who will be.

Mistakes have been made in this area before. Kristian Jaksch, Liam Sumner, Rhys Palmer and Billie Smedts are some of the many faces brought into the club recently that have failed to make their mark at Carlton. Compare that to Melbourne's recruitment hits, where the Demons snared players like Michael Hibberd and Jake Melksham for picks in the 20s.

The Blues need to find players capable of making a difference, who can arrive at little cost.

Mitch Wallis, Dom Tyson and Anthony Miles might find themselves 'gettable' at season's end. However, the club must be cautious and find the right targets, not just any targets.

Such upgrades in certain areas where the Blues desperately need improvements would then supplement the more high-profile names like Gaff and Sloane.

Carlton will also have a top-end draft pick. While midfielders have been targeted in the last two drafts, the Blues could turn their attentions back towards key-position youngsters.

Jack Lukosius and the King twins (Ben and Max) will be in Carlton's draft range and would complement the club's current crop of young forwards, led by Charlie Curnow and Harry McKay.

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With developing youngsters Jacob Weitering, Caleb Marchbank and Lachie Plowman down back, Carlton will be hopeful that spine is in place. Now it might be time to get creative.

Just like Melbourne did by shifting pick two to the Giants for Tyson and a later first-round selection in 2013, Carlton might need to move some pieces around to land genuine talent.

The Blues are likely to hold an early pick, so the other alternative for list boss Stephen Silvagni could be to shift that elsewhere to secure a star. The options are open.

When do we start judging the rebuild?

Right now, Melbourne fans would be pretty pleased with where the Demons sit.

Yet almost five years into their own rebuild, the club still doesn't have a finals appearance to show for their development. September footy appears inevitable in 2018, but it's taken time.

Such was the low base Carlton started from when Bolton took charge ahead of 2016, expecting the team to be challenging three years into his tenure is unrealistic.

Results have been poor, and performances like the one delivered last Saturday are unacceptable. Bolton would have reiterated such to his young side after the game.

But, fundamentally, this remains a team that won six games last year before losing arguably its two best players – Gibbs to Adelaide and Sam Docherty to injury.

Further injuries to Murphy and Matthew Kreuzer have also meant Carlton has been without its top four finishers from last year's best and fairest for large portions of the season.

The absence of Sam Docherty (right) has been keenly felt this season. Picture: AFL Photos

Kids, along with the team's subpar middle-tier, have subsequently been exposed.

Injuries to key players have not allowed Carlton to flick the switch offensively either, with the talent required to implement game plans trialled across the summer simply not up to scratch. The Blues have subsequently reverted to the more defensively-focused type of football played in Bolton's first two years in charge.

The way in which Bolton reduced opposition scoring from 107 points per game the year before he took over to 92.6 points per game last year is reminiscent of the way Roos took Melbourne's opposition scoring from 122.3 points per game to 90.5 in his tenure.

However, with that said, Carlton does need to start trending upwards – and soon.

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It will take Melbourne five years to return to finals, should it qualify this season. By that measure, Carlton will be targeting 2020 as the year they get serious about September.

Until then, judgements on the Blues and their 'reset' should be made cautiously. The footy world has seen how quickly things can turn. Just ask the Dogs and the Tigers.

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