What an odd device. But it would be a very handy thing to own back in the day.
Given that it would have been totally obsolete by, say, the 40's or 50's, it amazes me it survived...
Then again, those big round monstrosities that have been sleeping in people's basements for decades keep showing up on antique sites, offered by ever hopefull people who are certain they are worth a fortune, who have no thought to the fact that every middle class family in the country owned one, and they are not exactly rare.