When weighing yourself, take off shoes, sweaters, coats and start with light indoor clothing or as I suggested before, just underwear.
Eating is not an exact science and the knowledge we have regarding how the body uses calories or nutrients is not complete by any means. Depending on the formula one uses to calculate calorie requirements and the method of including physical activity, including exercise, varies greatly. I have used formulas that follow current nutrition science and practice in designing my calculator. However, the one subjective variable i.e. activity, can be over estimated by users.
In addition, bodies of the same gender, height and weight use calories differently depending on the amount of muscle vs fat. People with more muscle burn more calories than people with higher fat. Taller people burn more calories per pound of body weight than shorter people because the body has a larger surface area to keep warm. Some thin people seem to eat anything they want and not gain weight. While they may expel more calories as body heat, it is not understood why thin people can eat more calories and not gain weight.
Bottom line is, your weight is the sum result of what you eat and how many calories you expend, so don’t sweat the formulas to arrive at a calorie estimate. (BTW, stress factors like fever, trauma and surgery add to the calorie needs of an individual.) It is just that, an estimate or starting place. Use my calculator’s estimate for your calorie needs as a guide for your meals and snacks. If after a month you gain weight, then perhaps you overestimated your activity expenditure. If after a month you lose weight without wanting to, then perhaps you under estimated your activities. Adjust the calorie estimate up or down depending on what your weight is. As a female, don’t pay attention to 3-pound fluctuations in your weight if you are menstruating as small weight gains may reflect a shift in body water i.e. fluid retention.
Scales vary as well. Most scales are spring loaded and the spring becomes stretched with time and may not accurately record weight. Digital scales are similar, but with a digital display. The most accurate scale is a beam balance scale like your doctor uses. You don’t need to weight yourself daily, weekly is enough or you can tell about your weight by how your clothes fit.
Hope this helps.