the marble can also be used to check floors. in a basement it is usually hard to use the marble as the floor often is very rough, so use a water hose and wet the floor, any place the water sits is where the low spots are. this is great if you are wanting a level floor when finishing the basement, just add a cement leveler to the low spots, wait 2-3 days and check again. Just more little tricks taught me by my grandpappy's a half century or more ago. one was a master carpenter and the other a very good handyman
who built his own house and all the farm buildings himself.