Complex sentence: In an abbey or large monastery the dials were usually carfully carved in the stone walls, but in rural churches they were very often just scratched on the wall and it is sometimes difficult to distinguish them from graffiti.
Split into simpler sentences: In an abbey or large monastery the dials were usually carefully carved in the stone walls. In rural churches they were very often just scratched on the wall, and it is sometimes difficult to distinguish them from graffiti.