Digital Twins, sometimes known as digital surrogates, are attracting attention as a means to rapidly assess the current status of manufacturing enterprises. A digital twin models one or more aspects of a physical element so that it can be measured and optimized. A digital twin framework is a set of protocols and standards that can be used to assist the development, synchronization and measurement of digital twins. This paper contains an assessment of some early digital twin examples. They were submitted to Working Group 15 of ISO TC184/SC4 who are developing the ISO 23247 standard for Digital Twin manufacturing frameworks. The working group classified the examples into large, medium and small frameworks, and gave preliminary definitions to the protocols necessary to support digital twinning on the shop floor. The definitions were tested against a small-scale digital twin example, and measurements were made for the times and responses necessary to support real time digital twinning for machining processes.