ISO 17025 is applicable to all testing and calibration laboratories. Depending on the type of legal metrology activity, Legal Metrology Bodies could be accreditation under ISO 17020 if they are am Inspection Body, ISO 17024 if a Certification body and or ISO 17025 as a calibration laboratory.
As Legal Metrology is mandated by Legal Metrology Acts specific to a particular country, there may be other requirements that they need to meet in addition to 17025.
As a Legal Metrology Entity we are involve in both inspection and testing of measuring instruments to ensure compliance with Technical Regulations or Metrology Act. In that case which standards would be most applicable, the 17025 or 17025.
I assume you are asking about 17025 versus 17020? Legal metrology is the application of legal requirements to measurements and measuring instruments. ISO 17025 is applicable for calibration services in the metrology fields. ISO 17020 accreditation may be required, based on the type of inspections. This is because ISO/IEC 17020:2012 specifies requirements for the competence of bodies performing inspection whereas ISO/IEC 17025:2017 provides general requirements for the competence of testing and calibration laboratories. There are metrology components to Inspection so accreditation to IS0 17020 includes certain ISO 17025 components.
I suggest you with her to your country’s national legal metrology act and make contact with the national regulator of compulsory specifications, as there are typically registrations to be made that have other specific requirements. Also have a look at the International Organization of Legal Metrology (OIML) website at https://www.oiml.org/