In this paper we present ORBIT measurement framework and library (OML), which is a distributed software framework enabling real-time collection of data in a large distributed environment. The success of a multi-user distributed testbed facility depends largely on the ease of use, remote access as well as on the ease of collecting useful measurements from experimental runs. OML provides a flexible and dynamic way in which data is collected and made available for real-time access to the experimenters. Application programmers can use simple interfaces provided to transfer measurements and other performance data to a central repository. This paper focuses on the motivation, requirements, design, implementation and real world usage of OML that is designed to provide a scalable, controllable and easy to use mechanism for experimenters to collect useful results from the experiments conducted on the ORBIT testbed.