premise: The Chattenden and Upnor Railway (later known as the Lodge Hill and Upnor Railway) was a narrow gauge railway serving the military barracks and depot at Upnor and associated munitions and training depots. It was built in 1873 as a gauge railway, converted to narrow gauge around 1885, and continued in use until 1961.
hypothesis: The Chattenden and Upnor Railway was built more than 5000 days ago.
reason: It was built over 100 years ago and 5000 days is not even 20 years. It's difficult because I used 5000 days as the measurement.