How good a doctor do you need to be?

One aspect that I haven't yet seen tested in medicine is at what point would a doctor be considered negligent if he or she hadn't used a readily available and validated tool that, if used, could have changed the patient's outcome significantly? It may actually be the institution that employed the doctor that should be found culpable for not providing its clinicians with the necessary tools to do the job properly.

I am thinking, in particular, of the many modern clinical decision support or information tools that are now available but often either not available to or used by the clinician.

My own company produces a diagnosis checklist system which is validated, has been on the market for many years and is now even available as an app for as little as £1.99 that could save many patients from a delayed diagnosis. When could a patient reasonably expect a clinician to be considered negligent for not using these tools?