LPT: When cooking, you can weigh ingredients by how much you remove from a jar/container. Put the container on the scales and the amount removed will show as a negative value.

EDIT: It seems I wasn't clear enough that you need to tare the scales after putting the container on the scales. Then the exact amount you remove will be shown in negative. Example: Place a butter container on the scales, and press tare. Then remove 50g of butter and it will show on the scales as -50g.