Since blind people can't see the marks on the tape measure, they can't use ordinary tape measures properly. "The Sound of Length" conveys information about length to the user through the melody of the music. It works like a music box, every time the tape is pulled out 1cm, the product emits a tone, and ten different tones form a melody and repeat the cycle. This design allows blind people to use the tape measure in the same way as normal people, which promotes equality and respect among different groups of people. The beautiful melody can also relieve the anxiety of blind people.