I don't know which one is more trustworthy, I have a digital scale that I weigh on daily, and my mom has a mechanical scale, so when I go to her house I like to strip down to my undies and weigh myself there, and it's always 5lb less than the one at home.
I like that surprise and it makes me feel good about myself, but I stick to the weight on the digital scale, and when I reach my goal on my digital scale, I'll weigh myself on the mechanical one just for sh!ts and giggles