Listed in the Complete Collector's Guide to Pocket Calculators by Guy Ball and Bruce Flamm, Copyright However, they have the calculator as being made in Japan. My calculator is marked "Assembled in Singapore".
Vintage Omron Model 89M Handheld LED Electronic Calculator, Made in Singapore, Circa 1970s.
Vintage Miida LED Pocket Electronic Calculator, Model 828. Made in Japan, Circa 1974.