If you are weighing yourself at the same time of day each time you do, you can be a little more consistent in your comparisons as you tend to increase is weight over the course of the day as you eat & drink. But day to day, your weight can vary as much as 5-8 lbs due to water retention / loss. The more relevant number is your bodyfat because it will give you a better idea of what % of yoru weight is lean muscle mass and what % is bodyfat.