Libra Weight Manager - Weight tracking & BMI

Libra allows you to track your daily weight fluctuations and presents them in an engaging interactive chart.

• Enjoy the process of inputting your data on a daily basis

• Effortlessly navigate through your history with smooth dynamic charts

• Obtain quick analyses based on metrics such as BMI and body composition

• Set goals and estimate results for effective planning

• Share your chart with friends

• Safeguard your data in the Libra Cloud

• Seamlessly sync across all your devices

• Connect your Withings scale for real-time updates

Supporting Libra is more cost-effective than purchasing fast food!

Eliminate ads and access unlimited charts from friends for a nominal fee of just €1 (or equivalent currency) per month.

How forecasts are calculated

The forecast in Libra is an attempt at predicting the evolution of your weight based on its recent history.

The quality of the forecast is heavily dependent on the amount and quality of your recent data, though even the best forecast is only a rough estimation of the near future.

“Past performance is no guarantee of future results”

Calculation

In order to calculate the forecast, Libra takes all the entries inside the forecast window, which is configurable in Advanced Preferences and defaults to 7 days.

A best-fit line is then computed using simple linear regression over the trend values for each entry in the window, with the resulting slope representing the rate of weight change. This makes it easy to calculate a forecast weight for a given date, or the date at which a given weight will be reached e.g. goal weight.

Special cases

1. If there are only two values within the forecast window, Libra reverts to simple linear extrapolation of the line between the trends of both values.

2. If there is only one value, Libra interpolates the trend value at the start of the forecast window and uses that for linear extrapolation.

Notes

The use of the trend instead of the actual weight values is due to the noisy nature of the latter. Using pre-smoothed values avoids the forecast changing substantially on each new entry. Naturally this means that the forecast is affected by the trend smoothing configuration.

Libra’s forecast line only extends six months in the future. This was determined experimentally to be a happy medium between showing useful information while acknowledging that there will be variations in fitness and nutritional plans over longer periods of time.

The forecast line in Libra’s chart is drawn as a curve that continues from the trend line, and then smoothly points towards the predicted weight.

This can be confusing if the forecast line doesn’t cross your goal weight at the mathematically-predicted date: in those cases Libra trades mathematical precision for a more pleasant graphical interface.