Below is a chart for determining when an item was first registered
with the U.S. Patent Office.
For example, if you know the Patent No. of a clock is 109227, and wish to know the approximate date it was invented, you would be able to determine, by looking at the chart below, that this particular clock was patented in 1870. Patents are in effect for a specified number of years, so this may not be the date your item was actually manufactured, but it will at least give you an approximate date of invention.