Read the manual and search the datasheet for all occurences of OSCCAL.

From p12 of the manual:
Some PICmicro MCUs, such as PIC12C67x, PIC12CE67x and 12F6xx, have on-chip RC oscillators. These devices contain an oscillator calibration factor in the last location of code space. The on-chip oscillator may be fine-tuned by acquiring the data from this location and moving it into the OSCCAL register. Two DEFINEs have been created to perform this task automatically each time the program starts.

Define OSCCAL_1K 1 'Set OSCCAL for 1K device
Define OSCCAL_2K 1 'Set OSCCAL for 2K device
From the datasheet:
9.2.5.1 Calibrating the Internal Oscillator
A calibration instruction is programmed into the last location of program memory. This instruction is a RETLW XX, where the literal is the calibration value. The literal is placed in the OSCCAL register to set the calibration of the internal oscillator. Example 9-1 demonstrates how to calibrate the internal oscillator. For best operation, decouple (with capacitance) VDD and VSS as close to the device as possible.