Lifestyle tips

AFAIK most scales just have a 'zero out' option.

Only way to tell would be to grab something with an accurate weight and test it.

Another option is to get weighed by a professional device e.g. a weighing machine at a GPs.

With this you can check the accuracy of the two scales.

If you want to check your scale grab an unopened bag of sugar or flour and test it. They've got a known weight so results should match.

Some scales do allow adjustment, it's uncommon on digital scales but my mom's scale has it. If they have been adjusted it's usually to match the scale at their doctor's office scale.

Mechanical scales can also get off over time as springs wear or if they've been warped or bent. If grandma or someone in the family is near the limit that might have caused the discrepancy. I've personally caused that issue.

The other thing to check is that they're both on a hard, flat floor. If one is sitting on carpet you'll appear lighter.