When it comes to getting clear on scientific understanding there is no better source to consult than Henk W. de Regt's Understanding Scientific Understanding. It is no exaggeration to say that this book is by far the best philosophical treatment of the concept of scientific understanding yet produced.
Henk W. de Regt is Professor of Philosophy of Natural Sciences at the Instititute for Science in Society, Radboud University Nijmegen, The Netherlands.