A label side of a light-scribe optical disc includes a control feature zone recording therein reference information of the optical disc and a label zone to be marked based on the reference information. An optical head is moved in the label zone to determine a first FE gain and a first sub-beam addition (SBAD) signal by way of focusing servo technology. The optical head is further moved in the control feature zone to determine a second SBAD Signal. The first and second SBAD signals are operated to obtain a ratio. The ratio is used with the first FE gain to estimate a second FE gain for accessing to the control feature zone.