What is the legal test for probable cause in a search warrant application?

The existence of probable cause for issuing a search warrant is measured by a "totality-of-the-circumstances approach." (Illinois v. Gates, supra, 462 U.S. at p. 230.) "[P]robable cause is a fluid conceptturning on the assessment of probabilities in particular factual contextsnot readily, or even usefully, reduced to a neat set of legal rules." (Id. at p. 232.) "Finely-tuned standards such as proof beyond a reasonable doubt or by a preponderance of the evidence, useful in formal trials, have no place in the magistrate's decision. While an effort to fix some general, numerically precise degree of certainty corresponding to 'probable cause' may not be helpful, it is clear that 'only the probability, and not a prima facie showing, of criminal activity is the standard of probable cause.' [Citations.]" (Id. at p. 235.)