Simplify the following text for a Grade 7 native English-speaking person.
Original: Most slide rules consist of three linear strips of the same length , aligned in parallel and interlocked so that the central strip can be moved lengthwise relative to the other two .
Simplified: Most slide rules have three linear strips of the same length . The strips are aligned in parallel and interlocked so that the central strip can be moved lengthwise relative to the other two .