I've created an XL spreadsheet to update star coordinates from J2000 to the current date and time. Unfortunately, I have some issue after about 150 succesful formulae. My bug is somewhere in conversion to Local Hour Angle and dealing with refraction and then converting to Altitude/azimuth. Quite embarrasing after all that good work. This is not homework and I've checked the bugger using Meeus and now I'm just frustrated. If anyone is willing to take a look at the spreadsheet, I've attached a copy of the offending page. Any pointers in the proper direction would be MASSIVELY appreciated. Thanks, Scott. Edit; The bugger is too big to upload. Anyone interested in looking her over can e-mail me at firstname.lastname@example.org.