> the 'open("slope.txt","wb")' part but when I change "wb" to You want append('a') mode and you don't want binary mode('b') - you're writing strings after all! thus: open("slope.txt","a") Beware of eventually filling your disk with an enormous file tho... Maybe you want to create a new file every day/month/year etc? That way you can archive the old one... Alan G.