What constitutes reasonable diligence or "due diligence" under California Evidence Code section 240?

The term "reasonable diligence" or "due diligence" under Evidence Code section 240, subdivision (a)(5) "connotes persevering application, untiring efforts in good earnest, efforts of a substantial character. [Citations.]" (People v. Cromer, supra, 24 Cal.4th at p. 904, 103 Cal.Rptr.2d 23, 15 P.3d 243; id. at p. 898, 103 Cal.Rptr.2d 23, 15 P.3d 243 [reasonable diligence same as due diligence].) Considerations relevant to this inquiry include the timeliness of the search, the importance of the proffered testimony, and whether leads of the witness's possible location were competently explored. (Id. at p. 904, 103 Cal.Rptr.2d 23, 15 P.3d 243.) We independently review a trial court's due diligence determination. (Id. at p. 901, 103 Cal.Rptr.2d 23, 15 P.3d 243.)