It's not easy to track the effect of individual linemen on an offense.
There are ways, though, and it is particularly easy to see the impact Kyle Long has had on the Bears when he's healthy and starting.
The problem, of course, is he hasn't been entirely healthy since 2015.
Last year the Bears went through eight games without Long and got him back in time for the playoff loss as well as part of the regular-season finale against the Vikings. The foot injury he suffered followed a season-ending shoulder injury in 2017 and a horrific ankle injury in 2016. He also lost a game to a hip injury in 2014.
Long has failed to start 24 times in his 96-game career and his absence has been marked by reduced production in the running game.
When Long starts, the Bears average 112.7 yards rushing a game. When Long hasn't started, they averaged 103 yards a game.
A 9.7-yard average seems like very little, but consider a difference of this type last year separated the sixth-best rushing team in the NFL from the 15th best. The impact is obvious in those terms.
The loss of Long in pass blocking hasn't translated to more sacks. They've allowed 2.1 sacks per game with him and 2.2 without him.
Pass blocking is different in that teams can provide help for the backup lineman who is playing, or they can call plays differently in order to avoid longer pass drops.
The Bears struggled greatly to run without Long on the field initially last year when they tried to replace him with Eric Kush and then brought in Bryan Witzmann. They ran for only 64 yards against Buffalo's stout defense, and for only 54 and 38 yards in the two games with Detroit. In between, they had a 148-yard rushing game with only 89 of the yards coming from running backs.
So Long's health this year in the offseason, and continued health in the regular season could be critical.
With running backs David Montgomery and Mike Davis breaking into the back rotation this year for what will be a new offensive system to them, effective blocking will be critical.
When the Bears and Long reached agreement on a revamped contract in order to free up salary cap space, it caused general manager Ryan Pace to react: "We're excited that he's here and he's excited to be here and that's a long-term thing."
Considering the impact Long has on the running game, the excitement is understandable.