If you've studied Chinese before using Hack Chinese, there will be many words you already know.
There are two "obvious" (but poor!) approaches to how to deal with these words:
The problem with marking everything as memorized
If we marked them all as permanently memorized (option #1), in many cases, we would be overestimating your vocabulary and creating permanent gaps in your knowledge. For example, even if you tell us you've studied HSK 6 before, do you know with 100% certainty that you know every single word in HSK 6?
The problem with testing you on everything immediately
If we tested you on every word right away (option #2), it could take a very long time upfront, and would be very dull.
Instead, each day we test you on some of the words we assume you know. (You can set how many 'assumed known' words we check each day).
Because we only check a few daily, you can immediately focus on words that are much more likely to be new to you.
When we check your knowledge of a word we assumed you knew: