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Figuring out how modern-day offenses and defenses stack up against the units of the 1950s and '60s isn't exactly an easy task, but it's quite necessary when attempting to determine the best teams in each of the 30 current franchises' histories.

Just looking at points scored and allowed doesn't do the trick because that doesn't give pace an opportunity to come into play. For that reason, defensive and offensive ratings—pace-neutral metrics that show how many points a team allows and scores per 100 possessions—are much better gauges to measure prowess on those ends of the court.

But when attempting to rank teams historically, as we're doing here, that's still not good enough. After all, not every team with identical defensive ratings is on the same level. Nor is every team with an identical offensive rating equally competent at scoring the rock.

If two teams gave up 95 points per 100 possessions, which is worse—Team A, which did so during a year in which defenses rose to the top of the heap, or Team B, which did so when everyone was scoring points like the video game sliders were all the way up?

Team A should be the easy answer because context is crucially important. That, in a nutshell, is why DRtng+, or adjusted defensive rating, is the best inter-era metric for comparing defensive performances.

The same holds true for ORtng+ or adjusted offensive efficiency.

Calculating these metrics isn't particularly troublesome: Just divide the league-average defensive rating from the year in question by the team's defensive rating, then multiply the result by 100 to achieve DRtng+. Similarly, ORtng+ is derived by dividing the team's offensive rating by the league average and then multiplying by 100.

A score of 100 means the defense or offense was perfectly average that year. That does tend to happen fairly often, given that we're working with the 1,315 teams throughout league history for which we have data.

The final step in determining the strength of a team is averaging the two metrics. The result, called TeamRtng+, weights offense and defense evenly to ascertain the overall effectiveness of any team in NBA history.

When determining the top squads throughout the NBA's many seasons, the style of play doesn't factor into the equation. Neither does points scored or allowed per game. Nor does memorability, subjectivity or win-loss records.

TeamRtng+ is all that comes into play. We'll be looking at the best team in each franchise's history, counting down toward the best squad of all time. Analyses like this have been run before, notably by Hardwood Paroxysm's Andrew Lynch and Ian Levy, but this is taking it to a whole new level by calculating things before and after the 1976 ABA/NBA merger.

Note: All stats, unless otherwise indicated, come from Basketball-Reference.com. This introduction is an adapted form of what was used when ranking the top 20 offenses in NBA history as well as the top 20 defenses, bottom 20 defenses and bottom 20 offenses throughout the same period.