The invention provides scoring a performance of a guitar part in a rhythm-action game. It operates in the context of a video game platform in communication with a display and a controller and involves receiving an input performance from the controller including at least one input chord note, each input chord note including an input string value corresponding to a struck string and an input fret value associated with the input string value. Then, a reference performance is provided, which includes at least two reference chord notes to be input at a target time, each reference chord note including a reference string value and a reference fret value associated with the reference string value. Then, a degree of matching is determined between the input performance and the reference performance, and a score is assigned to the input performance based on the degree of matching.