Okay - using the chron package, I have solved a lot of my problems. I still get that peculiar result showing a two hour gap in the data at the position indicated below. Thanks, - Matt tide posit diffh y365 diftime 7223 -1.25 1901-10-28 22:00:00 -2.7 301 1 7224 -2.75 1901-10-28 23:00:00 -1.5 301 1 7225 -2.25 1901-10-29 00:00:00 0.5 302 1 7226 -0.25 1901-10-29 01:00:00 2.0 302 2 7227 2.65 1901-10-29 02:00:00 2.9 302 1 Any help or suggestions are greatly appreciated. Thanks, Matt -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._