  Reflection is an often addressed design goal in Human-Computer Interaction
(HCI) research. An increasing number of artefacts for reflection have been
developed in recent years. However, evaluating if and how an interactive
technology helps a user reflect is still complex. This makes it difficult to
compare artefacts (or prototypes) for reflection, impeding future design
efforts. To address this issue, we developed the \emph{Technology-Supported
Reflection Inventory} (TSRI), which is a scale that evaluates how effectively a
system supports reflection. We first created a list of possible scale items
based on past work in defining reflection. The items were then reviewed by
experts. Next, we performed exploratory factor analysis to reduce the scale to
its final length of nine items. Subsequently, we confirmed test-retest validity
of our instrument, as well as its construct validity. The TSRI enables
researchers and practitioners to compare prototypes designed to support
reflection.
