At Sixty Vocab, we believe retention is the key to language learning.  Our games’ time-based intervals are spaced for maximum retention. We’ll test you on each individual word once every 5 minutes, 1 hour, 1 day, 1 week, and at other intervals. If you can correctly identify words within 7 seconds, then your words will move up until you reach the top level. By the time you reach the top level, the words will be cemented into your long term memory.