I'm never sure how much estimating to do. This morning Ed Newman gave me tons of landfill trash projected from refuse contracts going back to 1973. The data points are for years the contracts were started, and do not include minor re-negotiations in the intervening years. For the Calculator I will place any missing years as the average of the years on either side. Landfill tonnage numbers since 2003 have been going up a lot, and Ed tells me that "around then" they started weighing the trash rather than estimating from volume.
There are dozens of different things that Campus Recycling collects and keeps out of the landfill (fluorescent bulbs, CFC gas, construction and development scrap, motor oil, toner cartridges, campus envelopes, etc) and they add more categories to that list each year. But what notes there are on quantities are in different units for each item (boxes of envelopes, crates of styrofoam, pickup trucks of reuseables) that I don't know how to convert to tons or cubic yards for comparison to trash. Ed showed me a conversion chart for items I'm willing to estimate. Still, data collection on that has been a lower priority than ITEM collection, and I'm missing data most years for everything not picked up by Athens Recycling. For the report I'll highlight a subset of years with relatively complete data and explain that there are probably similar numbers for other years. Doesn't change the Calculator tallies any, just how good we look.
Looking further into the calculator I found a column for Compost in the Offsets category! Compost just got much higher on my priority list, and will be a bigger part of my presentation.