To help level your bed using a comparison clock...

It will ensure that the bed is with the same height in all corners.

I recommend this comparison clock from "Mercado Livre" here in Brazil:
https://produto.mercadolivre.com.br/MLB-2640997037-relogio-preciso-comparador-0-10mm-de-001mm-_JM#position=14&search_layout=stack&type=item&tracking_id=7ae73b64-35b2-4b51-a9d7-de270fb6be15