平衡点

(setq skk-gengo-alist
      '((reiwa "令和" "R")
        (heisei "平成" "H")
        (showa "昭和" "S")
        (taisho "大正" "T")
        (meiji "明治" "M")))
(defun my:skk-ad-to-gengo-1 (ad &optional not-gannen)
  ;; Add "reiwa"
  (when (>= 1866 ad)
    (skk-error "分りません" "Unknown year"))
  (cons (cond ((>= 1911 ad)
               (setq ad (- ad 1867))
               (cdr (assq 'meiji skk-gengo-alist)))
              ((>= 1925 ad)
               (setq ad (- ad 1911))
               (cdr (assq 'taisho skk-gengo-alist)))
              ((>= 1988 ad)
               (setq ad (- ad 1925))
               (cdr (assq 'showa skk-gengo-alist)))
              ((>= 2018 ad)
               (setq ad (- ad 1988))
               (cdr (assq 'heisei skk-gengo-alist)))
              (t
               (setq ad (- ad 2018))
               (cdr (assq 'reiwa skk-gengo-alist))))
        (cond (not-gannen ad)
              ((= ad 1) "元")
              (t ad))))
(advice-add 'skk-ad-to-gengo-1 :override 'my:skk-ad-to-gengo-1)