I found an M/Z calculator online. The Calculator Academy Team signs responsible for the calculator.

Let’s take a look

You are supposed to enter the mass in Daltons and the charge into the calculator and it will calculate the mass-to-charge ratio. OK, but what are Daltons, and what is the charge?

Daltons

John Dalton is a famous scientist (chemist and physicist). Atomic theory was one of his subjects. The unified atomic mass unit (aka Dalton, Da, or u) was later named after him and is defined as 1/12 of the mass of an unbound, neutral, $Carbon_{12}$ which means that it does not and $C_{13}$ or $C_{14}$ isotopes.