There’s no score proper in either Infinifactory nor Spacechem, the game will simply tell you how many cycles your solution needs to complete the assigned task (time), of how many parts it is built out (blocks in Infinifactory, symbols in Spacechem), and how much room it needs to run (footprint in Infinifactory) or the number of reactors (single puzzle chambers) in Spacechem.
For each metric, the game plots a frequency (distribution) graph that shows every solution the game has collected, from all of the players: short bars are uncommon solutions, while taller are more common. The tallest bars are the typical solutions, though depending on the puzzle, there may be one or more.
Basically, you can think of them as par scores.
Your solution is shown as a vertical line imposed over the distribution. Left of the tallest bars is like saying better than most, the more to the left, the better the solution has fared. If it places on the right, then it’s under-performing.
Or, left below par, right above par.
Note that solutions can be optimized for one metric, so a fast solution may have a large footprint and require many a block, while a minimalistic solution may be slow.
Finally, the game shows you a small leaderboard composed by your friends only. You can read why the games are structured this way on Gamasutra.
SpaceChem’s histograms were developed as a replacement for global leaderboards. They solve two common problems:
Getting your name at the top of the leaderboards is a fantastic incentive for cheating.
For most players, the only thing a global leaderboard manages to tell you is that you suck (and not even by how much).
Unlike global leaderboards, SpaceChem’s histograms allow you to quickly and impersonally see how your solution stacks up against the aggregate. We have found that most players discover that their solution is terrible, but quickly formulate a personal challenge after looking at the histogram and replay the puzzle to improve their score. Because we include three antagonistic metrics (number of cycles, number of symbols, and number of reactors), players optimizing for one criterion often do poorly in the others, padding the graphs with low scores that make it easier to beat the average in a single category.
Of all the features in SpaceChem, the score histograms are probably one of the most popular, and one of my personal favorites. Considering that they’re not much more difficult than a leaderboard to implement, there’s no reason not to include them in your game and/or community platform – we’re looking at you, Steam!
I hope this answers your question, and in a way that isn’t oversimplistic nor too obscure.