; and (II) produces data that is interoperable with data collected by measurement to the standard soil depth in accordance with clause (i); (C) measure the core set of variables described in paragraph (5) to produce a standard set of reporting metrics; (D) produce data that is interoperable with other data collected by the Department of Agriculture; (E) account for calibration differences in soil analysis between testing facilities; (F) account for differences in uncertainty between different measurement tools; and (G) be usable for voluntary reporting of soil carbon data under subsection (b). (5) Core variables The methodology developed under paragraph (1) shall measure the following core set of variables for each sample: (A) Bulk density. (B) Organic carbon concentration. (C) Rock fraction volume and weight. (D) Other variables, as determined by the Secretary. (b) Voluntary soil carbon data reporting (1) Technical assistance (A) In general The Secretary, acting through the Chief of the Natural Resources Conservation Service, shall provide to producers described in paragraph (2) technical assistance, including guidance, for voluntarily measuring, monitoring, and reporting to the Secretary soil carbon data using the methodology developed under subsection (a). (B) Guidance Guidance provided under subparagraph (A) shall be, at a minimum— (i) available in multiple languages; and (ii) available to producers described in paragraph (2) in both digital and analog formats. (2) Applicability The guidance developed under paragraph (1) shall be applicable to— (A) producers that are recipients of grants under programs described in paragraph (3) to voluntarily measure, monitor, and report to the Secretary soil carbon outcomes under those programs