Spark-X2.5-1.7B: exact fee bases and half-up rounding study

Archival mirror of an existing public GERO publication, deposited 14 September 2026 to align platform coverage. This is an authored LLM arithmetic experiment, not an implementation-bug report. It retains 12 original paired exercises, exact arithmetic references, generated outputs and separate delivered-answer/full-stream scoring. The original score is 8/12 delivered answers; conclusions are limited to that authored set and recorded generations. No numerical experiments, source builds or current-upstream validation were rerun for this archival deposit. The report retains its original authorship, tested versions, duplicate-review scope, results and limitations; this is not a new finding or a claim of upstream acceptance, production exposure or customer loss. Prepared with AI assistance. Frozen publication repository: https://github.com/kadyrbekovhamit-cyber/spark-x25-financial-arithmetic-study/tree/37af701d16ce87aa0d6b8a284f416541f9b86048 . Full report: https://github.com/kadyrbekovhamit-cyber/gero-numerical-observatory/blob/main/catalog/reports/spark-x25-financial-arithmetic-study.md . GERO page: https://www.gero.uz/research/articles/spark-x25-financial-arithmetic-study.html . Original source, patches, quoted material and media retain their per-file and upstream licenses. Record-level licensing does not override those notices. See RIGHTS.md and the original repository notices.