Refer to figures. 
EASA learning objective 022.01.06.01.01 states: 'List and describe the following two parameters used to represent thrust: N1; EPR.'

EASA learning objective 022.01.06.01.02 states: 'Explain the operating principle of using an engine with EPR indication and explain the consequences of incorrect or missing EPR to the operation of the engine, including reverting to N1 mode.'

The thrust of a jet engine is measured in terms of N1 or EPR.

N1 - The rotational speed of the low pressure compressor fan. The faster the speed the higher the mass flow therefore the higher the thrust.

Engine Pressure Ratio (EPR) - This is the ratio of the turbine outlet(exhaust) pressure to the compressor entry pressure. This gives an indication of the acceleration given to the air by the engine, the higher the EPR the higher the thrust.

Not all turbojet aircraft use EPR as a method of measuring thrust, it depends on the type and manufacturer of the engine.