Virtual Instruments1 is an experimental programming environment for developing electronic test and measurement (T&M) applications. Intended users are test engineers, who are not programmers, but computer literate domain specialists. Unlike traditional programming environments, that provide weak support for a broad range of applications, virtual instruments provides strong support for a specific application. The programming paradigm is bottom-up synthesis of layers of virtual machines — called virtual instruments — using human interface models from the application domain, so that software development occurs without writing code. The object-oriented view of the world has proven a natural fit. Implementation was in Berkeley Smalltalk on a SUN workstation.