An extra curve on a log, designed to appear when the standard curve goes off track. For example, if the standard gamma ray curve is presented on a scale of 0 to 200 gAPI units, the backup curve may be scaled from 200 to 400 gAPI units. Alternatively, if the standard resistivity log is presented on a scale of 0 to 50 ohm-m, the backup curve might be presented on a scale of 0 to 500 ohm-m in the same track but be blanked off for readings below 50 ohm-m. The backup curve usually has the same coding as the standard curve but a different line weight.