Defines the distance (in degrees) between adjacent settlement measurement points. This value must be less than 45-degrees. API-653 Appendix B.1.3 requires at least eight points around the circumference of the tank. This limits the entry in this field to a maximum of 45 degrees. Additional data points will reduce the magnitude of this angle.
The software performs all computations using all of the specified measurement points. If the number of measurement points is so great as to cause the spacing to fall below 15 feet / 4.6m, use every other point when generating the input.
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The code limits the spacing between these measurement points (around the circumference of the tank) to 32 feet / 9.8 m. Prior to API-653 2nd Edition Addendum 2, this limit was 30 feet / 9.1m.
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Too many points may lead to an overly conservative determination of the out-of-plane deflection limit. Addendum 3 to the 9th Edition of API-653 suggests computing the deflection limit using points spaced at approximately 30 foot / 9.1m intervals. Additional details on this subject can be found in Out of Plane Settlement of Cylindrical Tanks by Erdmann and Yeigh, Hydrocarbon Engineering, May 1999 and the text by Phil Meyers, Above Ground Storage Tanks.