In an acoustic piano, pressing down a key causes the “hammer” (a felt-covered, mallet-like lever) to strike a string or group of strings, producing sound. Many digital pianos attempt to recreate the feeling of this mechanical action by adding “weight” (resistance) to each key. the simplest digital pianos are made to possess fully-weighted hammer action, and graded action. “Graded action” or progressive action, indicates that the keys at the lower end of the keyboard have slightly more resistance than the keys at upper end, mimicking the action of a true piano. Many cheaper digital keyboards are unweighted or semi-weighted, meaning they’re going to not feel almost like an acoustic piano.