The Vikings' backup quarterback needs to know where each step takes his eyes.

Each dropback, whether three, five or seven steps, is followed by a bounce forward — a hitch step. His eyes then need to find the first "read," or receiver's route designed to be open at that time. If he's not open, progress to the next read with another hitch step, and so on. Timing steps with routes is everything, as is vision.

Did you read the right coverage before the snap? Did you accurately anticipate on which read to pull the trigger? Is that receiver open enough? Is that defensive lineman about to maul you?

Complexity of the quarterback's job is why veteran Sean Mannion is the frontrunner for the No. 2 spot behind Kirk Cousins, whose 65-start streak ranks fifth among active NFL quarterbacks. But more often than not — 12 of the past 19 seasons, to be exact — the Vikings have started multiple quarterbacks during the regular season.

So for a franchise with Super Bowl aspirations, and one that made the NFC Championship Game two years ago with Case Keenum, the importance of the backup quarterback is not lost. Yet the salary cap-strapped Vikings find themselves with three unknowns — 53 NFL passes combined, all Mannion's — between the veteran Mannion, the third-year wild-card Kyle Sloter and undrafted rookie Jake Browning.

Competition is wide open, says coach Mike Zimmer, during Vikings training camp and the preseason.

"[Mannion] is a vet, so we're giving him a few more reps with the [second-team offense]," Zimmer said. "I don't think that job is locked down by anybody yet."

Mannion, the leader in the clubhouse, is the "fastball thrower" on a one-year contract signed in free agency. The 2015 third-round pick out of Oregon State spent the past four seasons backing up Rams quarterbacks from Keenum to Jared Goff. He cut his teeth under Rams coach Sean McVay, whose playbook was inspired, in part, by his time under Mike Shanahan with the Redskins.

Coordinator Kevin Stefanski and assistant head coach Gary Kubiak, brought into NFL coaching by Shanahan, have installed similar systems in Minnesota.

"There were a lot of similarities from what we were doing in LA the last few years to what we're doing now," Mannion said. "So I think just for there to be a little bit of familiarity with verbiage and concepts — obviously every system is going to have different details and different adjustments and stuff like that — but I guess in terms of my own knowledge of being able to pick it up quickly, I think that's helped."

Mannion's knowledge has brought clarity in meeting rooms.

"He can spit out answers a lot faster than a lot of them can," Zimmer said.

His on-time, deep touchdown throw to receiver Adam Thielen during Saturday's practice doesn't hurt.

But time will tell. Browning, a rookie out of Washington, and Sloter, a former college receiver in his fourth season playing quarterback, can alter the pecking order with a strong camp and preseason.

Sloter and Browning have shared minimal reps with the third-team offense. A lack of repetition is their struggle. They both get fewer practice snaps than Cousins and Mannion, so they need to shine with whatever they get.

Sloter, the Vikings' longest-tenured quarterback, arrived in September 2017 and has the reputation as an unstable practice player who thrives in games. Last summer, Sloter threw for three fourth-quarter touchdowns in two preseason wins, including a game-winning drive and two-point conversion against the Seahawks.

"I could fly by the seat of my pants and make plays," Sloter said. "But they want to see me operate the offense. Not just complete passes, which is a part of the game, but maybe not so much the gunslinger mentality. They want it to be calculated."

Read the defense, drop back and hitch forward through the progressions — that's where Sloter feels more comfortable in Year 3 with the Vikings. The process is also where coaches want to see efficiency, should he earn the backup job.

"I have to make the easy things easier," Sloter said.

Practices ramped up Sunday with the addition of pads, introducing real pass rushes and press coverage. Coaches will continue to watch how each backup quarterback handles the Vikings defense, from the pressure to the evolving coverages, ahead of next week's preseason opener at New Orleans.

"How he reacts to different things? How he gets checks in? And, obviously, playing in the game," Zimmer said. "So, we'll see."