US Patent 7530175 Twin level

A twin level assembly including two levels, wherein one of the two levels also contains an indicating device for performing a separate function, is disclosed. The twin level assembly comprises a first level and a second level that is selectively receivable into the first level through an opening in an end cap and into a receptacle of the first level. The second level is held in the first level by a retention mechanism. The first level and the second level each have at least one bubble vial for visually displaying level indications, while the indicating device in the second level is a type of stud sensor, laser pointer, metal detector, wire detector, or a sonic measurement device.