As most speed reader books are telling me, You start with reading one word. The you wil try to read two words at once. Then you will learn to read three wordt at once.
This can be implemented by making levels in the program.
Level one: One word
Level two: Two words
Level three: Three words
After that you can try to flash two and even three lines so the readers wil see in level four two lines (6 words) and in level five three lines (9 words)