In Measurement Based Admission Control (MBAC), the decision of accepting or rejecting a new flow is based on measurements of the current traffic. Since MBAC relies on measurements, an in-depth understanding of the measurement error and how it is affected by the underlying traffic is vital for the design of a robust MBAC. The consequence of the measurement error is that flows are accepted in error, a false acceptance and rejected in error, a false rejection. In this paper, the focus is on the prevention of false acceptance as the consequence is QoS violations and a service that may be of little use to the customers. Non-homogeneous flows cause increased complexity for the MBAC algorithm and also for the measurement process. The concept of similar flows is introduced, which is a restriction to simplify the analytical expressions in a non-homogeneous flow environment. This work differs significantly from previous work in the literature in that the measurement error is characterized as it abates with the length of the measurement window.