The diagram below shows darker colors for heavier keys and lighter colors for light weight keys. It only shows one octave for demonstration purposes, but the weight does gradually decrease in the piano as you go from left to right. However, you should only be able to notice a big difference in one end from the other. To find out how realistic your piano or keyboard is, play a couple of low keys with one hand and use a couple of fingers

and then immediately play very high keys on the right end and feel the weight difference. They should feel much lighter. The reasoning of this is very complex to explain and understand, so just think low-heavy, high-light. Of course, you realizing this is not all that important, but something you may want to watch out for when purchasing a new piano or keyboard.