HGC levels?

So my docotor did two blood draws about 48 hrs apart. They said it was 937 this first day then the second time I went in it was 3709. The doctor said that is good. but I still don't understand what it means. They said I could figure out roughly how far I am based off those number but didn't tell me? Also anyone have their numbers jump that high. The nurse said it was suppose to double and that's a bit more than double.