In the music industry negotiating the terms of net profit calculations for contracting purposes is necessary for establishing residual payments. Cassette sales residuals are the payments made to musicians, singers and other talents and to the personnel that made contributions to its production or use. How the residual is calculated may sometimes require extensive negotiations between the studio and the artists and other personnel. The residual is normally expressed as a percentage of the gross receipts. An attorney should be involved in the negotiations of the residual percentage because there is a lot of variation in the expenses that can be deducted from the gross revenues to reach a mutually agreeable percentage. Accurately determining those expenses and the payment terms of the residual amounts is necessary to insure the artists and technical personnel earn residuals and the formula is not calculated in a way that excludes them from ever being able to actually get paid residuals.