To determine which file you need for a particular loop, you must first know how many times per day that the chart is produced. You can find that information at the Available Products page.
You then need to determine how many days that you want in your loop. The available selections for most products are 3, 7, and 14 days. The two exceptions to this are the W Atlantic and E Pacific Wind & Wave Analyses. They both have selections of 3, 7, and 12 days.
The files are named descriptively. They mostly take the form of "OPC_Product_Loop_xX_Daily_xx_Day.html". The files for High Resolution products are exceptions to this. They take the form of "OPC_Product_Loop_Hires_xX_Daily_xx_Day.html", and MUST be used with High Resolution products. The first part of the name, "OPC_Product_Loop", is the generic beginning for all of the files. The next part of the filename, "xX_Daily", describes how many times per day that the chart is produced. For example, if I wanted to loop a chart that is produced 4 times per day, I would look for a file that has this format: "OPC_Product_Loop_4X_Daily_xx_Day.html". The next part of the filename, "xx_Day.html", describes the number of days in the loop. For example, if I wanted a chart to loop for 7 days, I would look for a file that has this format: "OPC_Product_Loop_xX_Daily_07_Day.html". Finally, the correct file for a 4-chart-per-day 7 day loop is: "OPC_Product_Loop_4X_Daily_07_Day.html".
High Resolution products have two additional options. The standard "OPC_Product_Loop_Hires_xX_Daily_xx_Day.html" files are suitable for a screensize of 1024 by 768 pixels. Two other sizes are available. The "OPC_Product_Loop_Hires_XL_xX_Daily_xx_Day.html" files are suitable for a screensize of 1280 by 1024 pixels, and the "OPC_Product_Loop_Hires_XXL_xX_Daily_xx_Day.html" files are suitable for a screensize of 1720 by 1260 pixels. You can load an image larger than your screensize, but you'll need to use your scroll bars to roam around the image.
www.nws.noaa.gov 
