First of all, I am not familiar with such a grading system. I speak for Germany, I don't know which country you come from as you didn't mention this.
In Germany, there are usually two types of employment contract, collective bargaining and non-collective bargaining.
For collective bargaining, rules are set by a contract between the union and the employers, which is available, it depends on a number of known factors and either you meet condition 𝑋 or you don't.
There are also non-tariff contracts, which are completely free. (A lawyer told me, that contract law is very free in Germany.) What you have agreed to with your employer applies, and that's that.
In addition, for grades, we typically have two systems, 1−6 (school degrees, where 1 is "very good" and 6 is "unsatisfactory"; in the US this compares to A—F), or exactly the other way round, 0 is "unsatisfactory" and 15 is "about very good". So, for a grading system, if there is such a thing, first of all you have to clarify which area is there, and what is good and what is bad. There can be both, so be careful and don't get confused.
Clarify the following question:
- Is the workplace paid according to a tariff?
Mostly, if that's the case, it's already in the job advertisement; because the collective agreement is usually a bit lower in payment, and I think they are also obliged to say that
If not, they should tell you all the rules, including which criteria for which standard you meet, or how far you meet them.
By the way, when I say contract law is very free, it also means that it is perfectly okay to negotiate about anything (and that is literally about everything). If you disagree with a point, discuss it. It is always more difficult to change something later in an existing contractual relationship than to agree something before a new contractual relationship. Be brave and you will see (if you are wanted—but about self-confidence is a psychological issue and would be a different question) that before contractual relationship, employers are surprisingly accommodating (because they want you). (That may not apply to everyday’s jobs like garbage collection, but it will surely apply to studied jobs in highly specific subjects.
I would like to tell another story here to give you courage: My uncle is a qualified physicist and was looking for a position as a university professor of physics. There aren't many of them. There were two places, one that he wanted and the other that he actually didn't want. Then he sent a message to the position he did not want, a kind of rejection offer, so to speak, if he should come here, he would expect so much (payment, high-tech equipment of laboratories, laboratory assistants, etc.) at least available. He was sure they would never approve this, but the university approved it! And today he works there and is very happy. Yes, it is abroad and the journey home is longer, but with more money, journeys by plane also become more convenient.
Basically, maybe I should have written that at the beginning, in German, the word "contract" (
Vertrag) is derived from "to agree" (
vertragen). In a contract, you should write everything in which you agree with your employer, even if it seems obvious and superfluous. That's what a contract is for. And that's what counts later. It is true that laws are above a contract and it depends on the jurisdication where you live, but you haven't written where you come from, so I can't answer for a specific jurisdiction.