A GPS receiver comprises a crystal oscillator with a manufacturer's characteristic curve, a GPS radio, a TCO temperature sensor, and a GPS receiver software. The crystal oscillator serves as a local reference oscillator for the GPS radio. The GPS receiver software instructs the GPS radio to search radio spectrum for GPS satellite transmissions. Once the combination locks onto a minimum number of GPS satellites and produces a user position fix, the precise crystal oscillator frequency can be measured and associated with a temperature reading from the TCO to software-compensate the local oscillator in later cold-start frequency searches. A "flat" SCXO model is piecemeal upgraded with individual calibrations as they are collected over the life of the GPS receiver. During manufacturing of the GPS receiver such flat-SCXO model begins as a device characteristic curve supplied by the crystal manufacturer.