There should be some checkpoints. It was fun but at the end of level 3 I new I would have to do alot if trial and error to get the codes working. It would be to boring to start all over numerous times so I stopped playing at that point. Maybe it's just me I'm just sayin.
There is a piece of paper (ripped into 3 parts) with the number on the paper and the instructions on how to enter the code... Sorry if that is a spoiler
Sure trial and error works but to work to get to the end just to die and start over many times for me is to boring. I wish there was a check point in that area. Some gamers are fantastic at doing puzzles and don't have that problem but a mere mortal like me......
For entering the codes no trial and error is required. If you look at the spoiler I posted above it will tell you how to enter the codes. Let me know if you need more information.