Here is how it works:

IEC 61400-12-1 Power performance measurements of electricity producing wind turbines
This IEC standard specifies the procedures for measuring the power curve. A key element of power performance testing is the measurement of wind speed for which the standard prescribes the use of cup anemometers. Hence, it also specifies the procedure for cup anemometer calibration. http://www.iec.ch

ISO/IEC 17025 General requirements for the competence of testing and calibration laboratories
This is the main ISO standard used by testing and calibration laboratories. In most major countries, ISO/IEC 17025 is the standard for which most labs must hold accreditation in order to be deemed technically competent. In many cases, suppliers and regulatory authorities will not accept test or calibration results from a lab that is not accredited. ISO 17025 does not relate to the anemometer but to the requirements for the competence of the laboratories calibrating it and utilizing it in a power performance test, respectively. http://www.iso.org

Measnet
MEASNET is a co-operation of companies which are engaged in the field of wind energy and want to ensure high quality measurements, uniform interpretation of standards and recommendations as well as interchangeability of results. http://www.measnet.com

Who is doing what?
WindSensor manufactures anemometers (BTW, the best on the market). WindSensor anemometers are classified according to IEC 61400-12-1:2005 Annex I.

WindSensor anemometers are calibrated in the SOH wind tunnel. The SOH wind tunnel is accredited according to ISO 17025 to calibrate anemometers according to the IEC 61400-12-1:2005 Annex F (BTW, with the lowest uncertainty on the market).

A number of testing institutes are accredited according to ISO 17025 to carry out power performance testing according to IEC 61400-12-1 using calibrated anemometers.