Think about it as every hour is equal to 50mph. There is a lot of driving at 75mph and a lot at 25mph so I use an average of 50mph. At 10 hours that is equivalent to 500 miles. All my Kubota manuals say 200 hours so that would be 10,000 miles which would be ok but I just change engine oil every even calendar year in the fall. Keeps thing simple and within the 200 hour mark.