I thought that the Shilling Scale for the rating of Scotch Ales was based on how much you had to pay for a pint. the Higher the alcohol the more you have to pay, assuming 10 shillings per ABV (70 shilling= 7abv etc.)
But after doing some research it was how much they had to pay per barrel of beer. in 1488 the first recorded sale of scotch ale went for 12 schillings/bbl. Plus there is a difference between Scottish and Scotch ales. Scottish ales called 60 (light), 70 (heavy), or 80 (export) shilling are in the range of 2.5 percent to 5.0 percent ABV. Scotch ale, or wee heavy, starts at 90 shilling and usually measures at least 6.5 percent ABV, with an original gravity of about 1.070. Some historical Scotch ales might be as high as 140 shilling, with a starting gravity of 1.125, although the scale has slid downward some over the last 150 years. Today's 80 shilling might be equivalent to a 60 shilling of 1850.
This information was taken from the following website if you want to read up on it fully.
Our Scotch Ale is 8-9% abv so we are calling it 80 Shilling this year. Looking over the history maybe if should be more of a 120 Shilling but hey we are in America not Scotland.