With the debut of the caliber 9SA5 in 2020, Grand Seiko introduced the most sophisticated mechanical movement it has ever produced and, on paper, one of the best mass-produced automatic movements in the market. Impressively engineered, the caliber 9SA5 accomplished the rare feat of both a high frequency and a long power reserve — conflicting traits that typically vary inversely to one another and don’t normally exist in spades in the same movement. This was achieved with the use of a brand new escapement, simply called the Dual Impulse.
While it was initially available in two limited edition models, the caliber 9SA5 eventually made its way into a regular production model — the 2021 Heritage Collection’s SLGH005 — making the Grand Seiko Dual Impulse Escapement only the second non-Swiss-lever escapement to achieve series production in a wristwatch after the co-axial.
Before delving into the weeds, it is worth revisiting the fundaments
