Once work is organized into work packages, we need a way to size each package. In steel erection, tonnage is usually the first quantity we reach for. It gives us a convenient way to spread the labor budget and track progress. The problem is that we do not make tonnage in the field. We make picks.
Two work packages can contain the same tonnage and require very different amounts of effort. One may consist of a smaller number of heavy, repetitive picks. The other may contain more pieces, more connections and more crane movements. The tonnage is the same, but the number of picks and the time required to complete them may be very different.
That does not mean piece count can simply replace tonnage. Not every piece is a pick, and not every pick behaves the same. Some pieces are erected individually, while others may be assembled or grouped before they are lifted. Some picks are repetitive, while others require substantially more rigging, coordination or setup. Defining what counts as a planned pick requires some judgment and a consistent set of rules.
Once that unit is defined, we can begin looking at throughput. Tonnage tells us how much weight was installed. Picks tell us how many installation events were required to produce it. Cycle time tells us how quickly the operation is moving through them.