about the actual value because you want to say was this a likely or unlikely run that I just saw happen then you can keep track of these in log space you can just keep track of the log probabilities instead of the actual probabilities and that way avoid the underflow alright so last thing to do if you do it this way is just a normalization but again as I said for numerical reasons often you'll be the new you'll be doing the normalization as you work along to make sure things stay in the range that your floating point is computation is happy