the best way is with a thermometer,but if you have thin chops this isn,t always the best way.i use the touch method,being in the business for 20 years i can touch a piece of meat and tell you what colour it is,try practicing.well done will be firm,medium will be a little mushy in the centre,med rare will be more soft to the touch.
good luck!
p.s
chefs tip...with your left hand,connect your index finger to your thumb and hold it loosely.press directly between the top knuckles of the finger and thumb(the fleshy part) this will feel like MR ,move a 1/2 inch towards your wrist and press,this is Med,another 1/2 inch and this is what well done will feel like.
good practice will help,try with all kinds of meat and eventually you will just know..