How to create local highscore

i saw numerous ways and tutorials to do local highscore,but non worked for me,it's says either NaN or it stays at 0.Can anyone help and tell me how to do it?

Try this one scirra.com/tutorials/37/beginners-guide-to-construct-2/page-6

I saw it,this is the first tutorial i saw and this tutorial who taught me construct 2,thanks to Ashley.i need u to tell me how to make local highscore or anyone.