you have to have a memory of what happened in the past and often important parts of that memory are dated they are pretty old and so when you're doing speech recognition for example and somebody says eleven then that's about half a second or something like that which means it's already fifty-eight time steps and another guy or the same guy says seven so the ending is the same Evan but now the system has to see the distinction between seven and eleven and the only way I can see the differences it has to store that fifty steps ago