CHICAGO — An author-held forwarded correspondence record preserves a message header dated September 26, 2021 and a general MQ statement about electromagnetic versus macroscopic determinations of the gravitational constant. It records a communication addressed to researchers associated with the National Institute of Standards and Technology (NIST) and CODATA. Its significance is documentary, rather than a new experimental result.

The date helps distinguish an earlier general proposal from a later interpretation of particular torsion-balance operating modes. It does not establish that the free-deflection and electrostatic-servo assignments used in the current MQ analysis were specified before the experimental results were examined. Figure 1 separates those claim levels.

The embedded original-message header gives September 26. A secondary account gave September 21; this archive follows the former. The Brief identifies the source as author-held forwarded correspondence, rather than treating it as a public institutional mail archive or a verified delivery record.

The public MQ account states that the apparatus-specific identification was made after examination of the BIPM/NIST measurement architecture. Free deflection is associated there with the count-resolved gravitational realization and electrostatic servo with the finite-count electromagnetic realization. That is MQ’s interpretation, not an assignment endorsed by the experimental team.

An addressed message alone establishes neither receipt and scientific agreement nor influence on experimental design. The reviewed record does not establish whether the correspondence affected the later work. Geiger’s reported lack of participation in experimental design, conduct or analysis must not be rewritten as an absence of prior contact.

The operating methods have their own experimental history. In free-deflection operation the pendulum’s motion is measured; in electrostatic-servo operation feedback holds its angle by applying a balancing torque. Both methods measure a gravitational interaction, and neither is a pure realization of only one type of physical metrology.

The companion Brief provides the chronology, source-access limits, technical meaning of the current regime distinction and the evidence needed for stronger priority or experimental claims. It keeps the 2021 communication, later apparatus mapping and subsequent quantitative comparisons separate.

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