This tutorial demonstrates how to reset any Casio Calculator, and should work on most other calculator brands.
Current deal on the newer version on this calculator (£5 in UK, $7 in US, $12 in AU)
UK: https://amzn.to/2Vxj62y
US: https://amzn.to/2LWkGq4
AU: https://amzn.to/2FdrHT8