The goal of live digital forensics is to collect crucial evidence that cannot be acquired under the well-known paradigm of post-mortem analysis. Volatile information in computer memory is ephemeral by definition and can be altered as a consequence of the live forensic approach. Every running tool on an investigated system leaves artifacts and changes the system state. This paper focuses on the understanding and measurement of the uncertainty related to the important and emerging paradigm of live forensic investigations. It also presents some practical examples related to the evaluation of uncertainty.