We chose to internally partition P&D probes into two main categories; experimental and calculated. Experimental denotes compounds from published probe characterisation experiments. These papers include profiling data for target modulation potency, selectivity, and possible secondary targets. Also important to note is that the experimental data largely originate from a single laboratory and are thus likely to have more consistent and reproducible data (e.g. where intra-laboratory assay variation is controlled via sufficient replicates and internal standards). Examples of such experimental probe sets include; Bromodomains chemical toolbox , Chemical Probes Portal 14 , Gray Laboratory Probes , Nature Chemical Biology Probes, Open Science Probes , opnMe Portal 38 , Protein methyltransferases chemical toolbox , and SGC Probes 12 .