You knew the Detroit Lions would be in scramble mode, trying to fill the void left by the now-retired Calvin Johnson.

They didn't wait long to take their first swing.

The Lions have reportedly agreed to terms with free agent wide receiver Marvin Jones, according to Dianna Marie Russini of ESPN. Jones was one of the top receivers on the market after a solid season with the Cincinnati Bengals, and he'll now team up with Golden Tate in trying to replace Megatron.

The question here isn't whether or not Jones can make up for all of Johnson's production as Johnson was still extremely productive his final two seasons. It's just how much he can help close the gap.

We'll try to answer this by using numberFire's Net Expected Points (NEP). This allows us to track the efficiency of teams and players, with the team totals being adjusted based on strength of opponent.

For wide receivers, we can look at either Reception NEP or Target NEP. Reception NEP measures the number of expected points a receiver added to the offense over the course of the year on all passes he caught. Target NEP takes into account the expected points lost on incompletions and interceptions on passes thrown that receiver's way. Using a combination of the both can help us track the effectiveness of a wide receiver and see how much they are able to aid their team.

Does this signing help out the Lions? Let's check it out.

Looking at Jones in 2015

There's a reason we look at both Reception NEP and Target NEP, and Jones helps illustrates the differences well.

If we zero in on just Reception NEP per target, Jones appears to be only a mediocre option. He finished 2015 ranked 34th in Reception NEP per target of the 48 receivers with at least 80 targets. This put him right between Kamar Aiken and Jordan Matthews. It's certainly not bad, but it doesn't blow you away.

He looks a good chunk better if we narrow the scope to just Target NEP. Out of that same group of receivers, Jones was 22nd in Target NEP per target. Again, this isn't going to tell you whether or not Jones will take off in Detroit, but he was at least mildly successful in 2015 after missing all of 2014 due to injury.

The issue here is quarterback play. Because both of these metrics will be affected by the quality of the quarterback, we need to view Jones' metrics relative to those of his teammates to nullify any gains he may receive from Andy Dalton.

This becomes especially true when looking at what Dalton did in 2015. He led the league in Passing NEP per drop back among the 46 quarterbacks who had at least 100 drop backs for the season. That's going to give Jones a big boost in these metrics relative to a receiver with a league-average quarterback (cough, Matthew Stafford, cough).

The table below compares Jones to A.J. Green and Mohamed Sanu, the other two wide receivers on the team who had at least 40 targets. It would be unfair to put his numbers up against Tyler Eifert as tight ends have different levels of efficiency than wide receivers.

Jones fell well behind Green, but that's exactly what you'd expect. Green had the third best Target NEP per target in the league, so that's a difficult comp. Jones did have double the efficiency of Sanu, though, which shows that it wasn't exclusively Dalton inflating Jones' efficiency this year.

Based on these numbers, it's pretty clear Jones isn't one of the league's elite options. However, he does at least look like a replacement-level guy who can provide you with some respectable production. Is that an upgrade over what the Lions currently have?

A Deep Hole After Johnson

If we were to do the same exercise as above with last year's Detroit receivers, it wouldn't quite be as glimmering. But we should do it anyway, just for funsies.

Stafford finished the year 18th in Passing NEP per drop back, landing him right in the middle of the pack. Based on this table, a lot of that production was because of what Johnson was able to do.

This is why it's fair to be concerned about Stafford's outlook without Johnson. Production dipped significantly when the ball wasn't going to Johnson, and they're not likely to find a straight-up replacement for that either in free agency or the draft.

Although Jones had a better Target NEP per target than Johnson, you have to remember the role the quarterback played in that. As such, we should be giving Johnson a considerable boost as Stafford on the whole wasn't nearly as efficient as Dalton, making Jones' numbers appear less impressive.

What Does the Jones Signing Mean?

It's hard to dislike this signing for the Lions. They obviously needed help at receiver with Johnson retiring, and Jones looks like he can help out. It's just not enough to completely salvage the Lions' passing offense.

In acquiring Jones, the Lions land a wide receiver who has been productive when healthy. He's not a superstar, but he's also likely as good as or better than what they currently have at wideout.

That doesn't mean the Lions should stop there, though. In Jones and Tate, the Lions seem to have two decent number-two options at wide receiver, but they lack a true top gun. They could attempt to fill that void via the draft as the free agent market isn't likely to provide much more than Jones, but that void definitely still exists.

Ignoring the free agent market would have been a mistake for Detroit considering how great Johnson was, and Jones seems to have earned the reputation as one of the better receivers available. He may not completely keep the Lions' offense afloat, but Jones is at least a good first step in the Lions' quest to keep slinging it effectively.