1/5/2009 Midnight Time Correction Exercise Page 2 of 3

Using the “Meteorological Data Operations” help document for directions, you will import meteorological data from a sampler into the Toolbox. The “midnight time correction.txt” file contains data that have been downloaded from a meteorological sampler (SamplerID INMET) at the Tribal Air Office site (Site ID S001), for the biweekly sampling period starting on 08/08/2007 at 8 AM. The sampling times in this file are start times.

(Remember to work from a copy of your toolbox-after-exercise-4 file, so that you can go back to that file and begin this exercise again if you do not complete it successfully the first time.)

Look at the data file, and think about whether the time shown as midnight is really midnight of that same day. The way to tell whether the midnight time correction needs to be done is to look at the first value in a day. Sometimes, as is in this dataset, the first full day is not at the beginning of the dataset (this dataset starts at 8 am). If Access is not told which day the midnight value is associated with, it may put the first midnight value at midnight of the first day, before this 8 am time. This can be understood better by looking at the following graphs.

If the times in your file are START times, and the first hour of a new date is 01:00, then the correction should be done (because then the 00:00 time prior to the 01:00 time is midnight of that new date). However, if the first hour of a new date is 00:00 (and times are start times), then the correction doesn’t have to be done.

You can see that ideally, times are logged 00:00 as midnight of date 1, thru 23:00 of date 1, and THEN the times roll over into the new day, so that day 2 has its first time logged as midnight (00:00) through 23:00.

This can be seen more clearly by looking at the data. You can see that the values for the 24:00 rows in this small data set contain 999999999 values, which make them easy to identify. Then, find the first value for each day. Is it 1:00? If yes, the midnight time correction needs to be run. In this case, the first value for the day (day 221, as opposed to day 220 which is incomplete as it only started at 8 am) is 1:00, so the midnight time correction needs to be run.

If you imported this dataset and did not run the midnight time correction, Access would think that these values are from the wrong day.

Import the data from the file “midnight time correction.txt.” Go thru the exercise without pressing the time correction button. When you have gone completely through the import process and gotten the data into the archive table, open the archive table. This is done by pressing F11 and then finding the tblDataArchive in the left view objects pane.

and note the dates of the 999999999 and the 888888888888 values. where these values are in the Verification table. Now, go back and click the time correction button so that they are put into the correct day.

After you have completed this import, close the Toolbox. Then, make a copy of the Toolbox and save it in the “SUCCESS” folder (within the “ToolboxCourseExercises” folder) on your computer. Name the zip file “Toolbox_ExMIDNIGHT TIME CORRECTION.” Online students should attach this file to the assignment.

Revised 1/7/2009