The meat thermometer probably does not show correct surface temperature, being round and surface flat etc.
The thermistor table in firmware contains one adc column and one temperature column. The firmware reads the adc value and translates it to temperature by the use of that thermistor table. You can calibrate the thermistor table manually. You can take each row, and from the table that is uploaded in firmware, set the temperature in the row, to trick the system to reach the corresponding adc value. Then you measure that point with a real life temperature tool (preferably a multimeter with a termocouple), and write that real value down for each row. Then you replace the old table temperatures with your own temperatures and do the firmware upload again. And double check etc.
The thermistor table in firmware contains one adc column and one temperature column. The firmware reads the adc value and translates it to temperature by the use of that thermistor table. You can calibrate the thermistor table manually. You can take each row, and from the table that is uploaded in firmware, set the temperature in the row, to trick the system to reach the corresponding adc value. Then you measure that point with a real life temperature tool (preferably a multimeter with a termocouple), and write that real value down for each row. Then you replace the old table temperatures with your own temperatures and do the firmware upload again. And double check etc.