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It is important to check the return valuein value in IRET to ensure the call has been successful.
In the special case when the specification for the output field is identical to that of the input field, interpolation is not carried out. This is an important optimisation for MARS processing and is indicated by a combination of return values in IRET and OUTLEN (both are set to zero).
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- IRET = 0
- OUTLEN = 0
- OUTGRIB does not contain the `new' field since it already exists in INGRIB