temperature

Generally speaking, a thermometer is most accurate. Some electric kettles have temperature settings so you don’t need a thermometer.

Many people also use a cooling pitcher (samashi) to manage the temperature of water without having to use a thermometer each time. Not sure if you’re familiar with this practice. If you don’t have a samashi, you can use a spare mug or other small pitcher. Basically when water boils it reaches 100 degrees Celsius. Pouring it into the cooling pitcher drops the temperature a few degrees Celsius. Then when you pour it into your teapot, the temperature drops a little more, reaching the ideal temperature for green tea. I wouldn’t fuss over exact temperatures, as long as you’re in the ballpark.

Best rule of thumb is to avoid pouring boiling water directly on greens, it can diminish the quality of the tea and give you flavors you may not desire.

Here’s a good tutorial.
https://youtu.be/KoLzqUfIpSo

before I got a variable temp kettle, I didn’t have a thermometer so I did the math and figured out how much room temperature water I had to add to the boiling water to make it the desired temperature