There is a list of differences in civ5 difficulties here: http://www.civfanatics.com/civ5/difficulties
What does "Production Free Units" row mean?
There is a list of differences in civ5 difficulties here: http://www.civfanatics.com/civ5/difficulties
What does "Production Free Units" row mean?
Production free units is NOT the number of units you can have without maintenance. It is the max number of units you can support without suffering a production penalty in all your cities. This production penalty rarely kicks in unless players build giant armies so many people are unaware that it exists, mostly because maintaining a big enough army is too expensive due to the exponential costs. For each unit over that limit you lose 10 percent production to a maximum of 70 percent. You can see this penalty in the top UI bar if it triggers as a -10
The calculation for unit cap is based on difficulty, which is what you are seeing. Max units without penalty is equal to Production free base units + (production free units per city * number of cities) + number of citizens. So on deity it is 5 units, plus 2 per city, plus 1 per citizen.