Effective way to remember learned from the Forgetting Curve
From time to time, I get the question:
What is the best way to remember new words?
I confess that I had ignored the question, and I had not researched or thought through the question. One day, I finally spent some time on research. I had always thought I was bad at remembering new words. After some research, it seems that the truth is more that I forget quickly.
Hermann Ebbinghaus
From 1880 to 1885, German psychologist Hermann Ebbinghaus ran a limited, incomplete study on himself. He discovered the forgetting curve and the spacing effect. He was also the first person to describe the learning curve.Forgetting curve
According to Ebbinghaus' study, people forget 42 percent of the things they remember in 20 minutes. An hour later, they forgot 56 percent. In 6 days, they forget 75 percent.
Ebbinghaus studied the memorization of nonsense syllables, such as "WID" and "ZOF". Applying this study to remember any subjects could be irrational. Even though, it is apparent that people forget more in a long time. What surprised me is people may forget even in a short time more than I thought.

Spacing Effect
The spacing effect demonstrates that learning is more effective when study sessions are spaced out.
The research tells that it can not be a good idea to memorize a lot of things in a short time period. (Massed practice / Cramming)
It is better to keep studying with some breaks for a long time if people want to memorize better. (Spaced practice / Distributed practice)

Put ideas into the Wordbook
I got an idea to improve the Wordbook with those theories. The default sort option (Training Mode) in the Archive is implemented with the idea.
The words users don't remember yet are shown prioritized. Among the same level of memorizing the words, the words users don't check out less frequently are shown prioritized.
When users check the details of the words, the app counts how many times they have checked each word. Users can see how many times they have checked words and when the last time they checked was.
This function helps me a lot in memorizing words.