The degree of reuse from system to system is measured by the number of times services are reused. This can be represented as a percentage of reused code to overall application code. A simple approach might be to look at the percentage of reused services against the total number of services. However, this neglects the relative programming effort that goes into the different services.
A more accurate metric is to look at the function point count of reused services in relation to the total function point count. Reusing a complex service many times can provide a greater return on investment (ROI) than reusing a larger number of simple services a few times.