The long-used, highly-endorsed gauge created by former Cowboys coach Jimmy Johnson to rank the value of draft picks has some competition now. (Brian Wicker — Islamorada Times/The Minnesota Star Tribune)

When Jerry Angelo, the former general manager of the Chicago Bears, got a phone call from one of his colleagues inquiring about moving up or down in the draft, there was one document Angelo consulted to gauge the value of the potential deal.

It's a document that has had staying power across the NFL since the early 1990s and has withstood changes to the game, the salary cap and the draft itself — the Jimmy Johnson trade chart.

Developed by the former Cowboys coach, the chart assigns a point value to every pick in the draft and serves as a guide for teams attempting to make trades. If you want to trade for the No. 1 pick in the draft, valued at 3,000 points, you better be willing to fork over 3,000 points worth of picks.

"It lets you cut through all that red tape," Angelo said. "Everybody agreed that they would use it and it was objective and everybody was playing off the same deck. I thought it was great. I saw no holes."

Johnson devised his values on how teams traded picks in previous drafts, and his chart became the primary tool front offices used when negotiating and trading picks. Angelo said assigning a value to picks was once a draft-day disaster for GMs.

"That was a real pain to do," Angelo said. "Once everybody looked at [Johnson's chart], it was like osmosis, we all just agreed that this was the way to go."

The Johnson chart lives on today. Analysts and bloggers will use it later this week to judge whether teams won or lost a draft-picks trade, but not everyone sees it as gospel like Angelo does.

More recently, teams and others have been devising their own pick value charts. Some see a weakness in Johnson's chart in that it doesn't account for the expected production of players in each draft slot. One popular chart in the analytics community takes a different approach: it attempts to calculate the expected production from a pick's first five years, or the maximum length of a rookie deal for first-round picks.

This chart, created by Chase Stuart of footballperspective.com, revolves around a unique statistic Profootballrerence.com uses to compare players across positions — approximate value (AV), a catch-all statistic, à la wins above replacement (WAR) in baseball.

AV mixes traditional statistics — touchdowns, yards, etc. — with team-based performance to come up with a number for each player. It's not a foolproof statistic, Stuart said, but it is one of the best ways statisticians can compare a wide number of players, regardless of position and era.

"There's a lot of weaknesses and a lot of strengths," Stuart said. "It's heavy on the approximate. … It's perfect for a study like [the draft], which is measuring large groups."

Stuart's pick values differ from Johnson's in a couple of important areas — Johnson's chart tends to value picks at the top of the first round more and value picks in later rounds less, especially the second and third rounds.

On Johnson's chart, the No. 1 pick is worth 3,000 points. Stuart calculated that the No. 1 pick has been worth an average of 34.6 AV in the first five years of the deal, which converts to 1,463.6 points on Johnson's chart, Stuart said.

Johnson's values fall sharply from the top of the first round, but Stuart's chart still values first-round picks lower than Johnson does. The charts are almost equal around pick No. 48, and from there the value on Johnson's decreases at a faster rate. Stuart's chart says second- and third-round picks have significantly more value based on their expected output than Johnson's chart would indicate. This could be why some teams, such as the Patriots, have made a habit of trading down in the draft as much as they can.

"First-round picks and high first-round picks tend to be more valuable early in their careers," Stuart said. "So I think some of it is immediacy. If you want an immediate contributor, the difference between a first-round pick and second-round pick is probably bigger than my chart tells you. But in year three, it's probably smaller than you think."

Teams can skew the value of a pick if a team is trying to move up to get a quarterback, especially under the terms of the current collective bargaining agreement in which rookie salaries are slotted.

Prior to this CBA, which features four-year contracts with a team fifth-year option for first-round selections, top-end picks could cost a lot of money. Sam Bradford, the No. 1 pick in 2010, signed a six-year, $78 million deal ($50 million guaranteed) with the Rams. In 2016, the Rams traded up to draft Jared Goff No. 1 and signed him to a four-year deal worth only about $28 million.

"The fact that the picks are slotted financially, now the [top] picks to me have more value because you're not having to pay exorbitant money," Angelo said.

Especially if you can get a franchise quarterback who might outperform his rookie deal, allowing you to build a roster around him.

Come Thursday, there will be trades — many of them — in this year's draft. But even if a team has its own draft chart, the starting point for any negotiation Angelo and Stuart said, is still the Johnson chart.

"It sets the market so people can at least understand it," Stuart said. "It gives people who are trading draft picks a currency. If you don't know the currency, it's hard to trade."

But getting the most bang for your buck might depend on which chart you like better.

Chris Hine is the lead writer for North Score, the Star Tribune's sports analytics beat. startribune.com/northscore. E-mail: chris.hine@startribune.com