Don't want your Google search results filled with incomprehensible garble? Google Operating System notes that you can customise English-language search results to include only documents with a given readability level.
To access the feature, you need to click 'Advanced search' on the main Google page -- it isn't a filter option for standard results.
While Google hasn't identified the specific scale it uses, you can choose basic, intermediate or advanced. Basic might well be useful if you're looking for information for your kids, while advanced could help single out academic and scientific material. Not necessarily helpful if you just want a cheap external hard drive or hotel room, but useful for more detailed research.
Google Shows Reading Levels for Search Results [Google Operating System]