Leave the NitroSense dashboard open on a second monitor. The lets you reset the "Max Temperature" log. Run Cinebench or 3DMark and press the button after the test to see your peak temp.
Mastering the NitroSense Key: Your Guide to Acer Performance Tuning nitrosense key
The key acts as a quick launch for the NitroSense application, which allows you to: Leave the NitroSense dashboard open on a second monitor