When scientists in the 1960s - 70s compiled data to build their global average temperature series they used state averages of monthly mean temperatures from weather stations around the world. (skepticalscience.com)
I also create yearly files of monthly means for when I need a long - term average. (hannahlab.org)
After all, how can paying weekly instead of monthly mean the equivalent of one extra monthly payment? (moneysense.ca)