How do you calculate fat percentage and muscle mass. Is there a way that does not involve expensive equipment?
In most cases any measurement instrument will do, you just want a number to track even if it’s grossly inaccurate.
I can confirm that even the cheap digital scales will give you the trend with the same approximate shape as high quality measuring systems. If you have enough data points (like measuring 1-2 times per day or over a long period) any outlier will be excluded and the overall trend will be very close to reality. Which is enough for all intents and purposes.