Dive summary:

• Sometimes things go far enough off-track in a project that a contractor feels it's essential to seek more compensation because of delays imposed by outside circumstances, and the critical question then is how will a court or arbiter decide what's owed.
• Having kept good records for the project involved and for similar work done elsewhere will be a huge help if the standard is the commonly  used "measured mile."
• The standard is easily expressed – what was the cost in man-hours of money of similar work done without delays – but it's important to be as "similar" as possible, including location, kind of work, season and any factors that the other side could use to challenge the comparison.

From the article:

Whenever these types of events occur on larger construction projects, there is usually a substantial loss of productivity. Yet, contractors are frequently unable to prove the appropriate amount. ...