That’s the age of this house,
located in North Tacoma. It had many of the quirks that come with homes of this age: originally built with no bathrooms, a questionable foundation… and floors up to 8 inches out of level, requiring careful measuring, shimming, and sheeting.
The clients, who had just purchased the home, wanted real hardwood floors installed. This meant that the subfloor only had to be reasonably flat from one end to the other.
Being perfectly level isn’t a requirement.