Writing this blog motivates me to regularly prune and update my collection of basic tools, and if they are in a book, see if there is a web-based version of the same or better quality.
Today as I was recording lab values for my tube feeding patients, I decided to look for online interpretation tools. I really like the Merck Manual's chapter on Fluid and Electrolyte Metabolism. The information is well-organized and explained clearly and concisely.
This guide on converting conventional units to Système International d'Unités (SI) or international units (IU) also would be useful to refer to when reading the literature.