ALLEN PARK, Mich. -- Matthew Stafford doesn't believe he is any faster than a season ago. Didn't think he made any physical improvements, either. Doesn't think he is "any more jacked," either.

The sixth-year Detroit Lions quarterback is the same as he was physically. It is everywhere else, possibly, where the former No. 1 pick has changed.

Off the field, he became engaged to his longtime girlfriend, Kelly Hall. On the field, he also possibly engaged a bit more, having to learn a new offense and new terminology for the second time in his professional career.

It was that engagement on the field that caught new coach Jim Caldwell's attention almost immediately.

"He left this spring with I think a real solid understanding of what we're doing from an offensive standpoint," Caldwell said. "He came back this fall further ahead than when he left. That tells me that he studied.

"That he obviously dedicated himself to getting better and he's moving at a pretty rapid pace in terms of doing a lot of the nuances that come along with operating this particular offense."

It is this offense that gave some of the Lions some issues early on, from the longer terminology insisted upon by new offensive coordinator Joe Lombardi to the change in routes run from certain positions and how many yards a certain route is supposed to be run.

Add in a new receiver -- Golden Tate -- and a first-round rookie tight end in Eric Ebron and there are timing issues to secure as well.

Stafford has apparently handled it all comfortably both in practice -- where he had an interception-less streak lasting almost two weeks -- and in his first real action, where he was 9 of 10 passing with his lone incompletion dropped by Reggie Bush.

"For me, the biggest challenge this offseason was trying to get the mastery of the playbook, the new system we have coming in," Stafford said. "So that's what I spent most of my time and effort on and with that comes new drops and new reads and things like that.

"I don't know if there's one thing that stands out to me. Just being an overall better player."

That had to happen, though, because Stafford realized from the day he stepped into the Lions facility in 2009 as the No. 1 overall pick the franchise would largely succeed or fail based on his play.

He looked at the commonalities among playoff teams and one of the things he noticed was the proficiency of the quarterbacks who made runs to conference championship games and Super Bowls. He understood he would have to attain a certain level in order to provide that for the Lions.

He said Tuesday he has always held himself to similar standards -- and his measure of that is the points the Lions score and how few turnovers he ends up responsible for. Those were numbers Detroit -- and Stafford -- struggled with in the latter half of 2013, when Stafford threw 13 touchdowns, 13 interceptions and had the No. 31 passer rating in the NFL over his final eight games.

His interpretation of high level -- something he clearly didn't achieve last season -- remains constant.

"It's tough to put numbers on it," Stafford said. "You just want to go out there and make good throws, make good decisions, limit turnovers, make sure we're in the right play every time if you can and with the team, that's the biggest thing."

If he does that, then he should have a season closer to 2011, when he was considered one of the brighter young quarterbacks in the NFL. Stafford may still be young from an age standpoint at 26, but he is also entering the prime of his career.

Six seasons in and the Lions shouldn't see the same movie from Stafford as they did last season. After the supposed improvements his new coaches made, they should see a sleeker, sharper version. The early results have indicated this as well.

"He's worked at it extremely hard," Caldwell said. "Often times you'll find guys will look for an excuse why they weren't as effective in certain phases. Hey we got a new system, it's real tough, learning curve is a little difficult. He's made none of those.

"He came out, he's worked, he's functioned and he's gotten better as a result of that and I look forward to him just keep improving."