The Catholometer is a method of measurement Luke came up with to rate how understandable his stories are to those with varying levels of experience and understanding of the Catholic faith. This doesn't mean that only Catholics can read his articles nor should you be prevented from reading something because you think it might be too hard (or too simple) to understand, but that you should have an idea of what to expect before you dive into the topic.
The first step on the Catholometer denotes articles that should be understandable to the general public, regardless of belief. This may also signify articles that have little to do directly with Catholicism. They presuppose a general knowledge of spirituality and a recognition of a higher power.
The second step on the Catholometer reflects an article that would be understood by the average Christian reader or someone who has a general knowledge of the Church's central teachings. It may contain hints of theology, but may focus more on broad aspects of spirituality. They presuppose a general knowledge of Christianity and a desire for relationship with God.
The third step on the Catholometer reflects those stories that contain slightly deeper theological points and/or meditations. They presuppose a general knowledge of the faith and a lived relationship with God.
The fourth step on the Catholometer is when we dive into deeper concepts of Catholic theology and spirituality. They may include research into topics gathered from other sources. They presuppose an advanced experience of a lived relationship with God and are geared toward those seeking to take their Catholic faith to the next level.
The fifth and final step on the Catholometer is for those who want to be a Saint. Tough concepts of the Catholic faith may be discussed. They may contain meditations and discussions on higher-level theology, with adequate research to bolster the reflection. They presuppose a lifetime of a lived relationship with God.