Full text
if the use regularly made of the property for the purpose of gaining or producing income has decreased, the taxpayer shall be deemed to have disposed at that time of depreciable property of that class and the proceeds of disposition shall be deemed to be an amount equal to the proportion of the fair market value of the property as of that time that the amount of the decrease in the use regularly made by the taxpayer of the property for that purpose is of the whole use regularly made of the property;