Looks like they didn't have rulers, string or plumb  bob's.  Just like our house.

I've thought multiple times that they (builders of homes like ours) could have broken a stick off and used it to make even spacing for floor joists and ceiling joists and they could have tied a rock on a string to make the walls perpendicular to the earth.

Just to be clear, many of our joists are spaced differently from end to end and side to side nor all all the walls vertical.  It's always irritating to work on our house if you want a square corner.

Nails must have been cheap because sometimes I found 6 or seven nailed to a 2X4 on just one end.