Alright, some knowledge.
A TDS Meter is a Total Dissolved Solids measuring tool. It tells you how many Parts Per Million of any Dissolved Solids are within the solution. With that being said, TDS and PPM meteres are one and the same. PPM is the measurement.
Now possibly your friend gave you an EC meter, and that could be throwing you off. EC is Electrical conductivity and measure how well a solution can conduct an electrical signal sent through it.
Can you give us some model numbers or pictures to help us help you?