In Opus Magnum, your solutions are graded on three factors: cost, number of cycles, and area. The first is very simple: it's the sum total for all the parts you used. The second is also straight forward: it's the number on instructions that were needed to produce the required number of molecules.
The third has me confused, though. I don't understand how the area metric is calculated. It's not simply the number of hexes occupied by your parts, nor does it seem like it's just the area ever occupied by part or element, although that does seem to be closer to the truth.
So, how exactly is the area of a solution calculated?
Area calcuation is based on the final amount of hexes your contraption uses after being run, including arms or parts moving outside the initial area of the contraption.
As you can see the area taken up by the contraption (without running it), is 7. However, once started, it moves over 2 additional hexes, making the total area count 9.
During simulation, pressing
2 can provide additional stats on your contraption.
It's the number of hexes occupied, but it's often larger than you might think due to rotations (any partly-occupied hex counts).
To study the area, start your solution and press and hold the button in the group of four in the lower right, or the 2 key. This will highlight every hex that has been occupied so far with a blue outline.
Example: In these pictures, the arm 4 rotated to the left. The hex immediately to the right of the arm becomes occupied because the arm crosses it (even though this does not collide with anything) and the bottom-rightmost highlighted hex becomes occupied because the atoms passed through it (even though this was during a rotation operation, not on at the beginning or end of it).
Area-optimized solutions often contain very few arms with long programs, because every additional arm is an additional hex occupied permanently by an arm base.