Weight is pretty much a useless metric if you are already slim and want to find out when you are going to start seeing definition (like your abdominals for example). Body Fat % is really the only indicator for that and even then it is hit or miss as it depends on the elasticity of the persons skin (like if they just lost 100 lb''s they'll have a ton of excess skin covering their abs). Cool site, i'd just like to see BF% instead of weight.