Measure out about 1000g of water. Since 1g = 1ml, you can also use 1000ml or 1L.
Grind about 45g of fresh coffee. The grind you're shooting for is just finer than a french press grind.
Unfold the chemex filter and place the side with 3 layers on the spout of the Chemex. This allows air to escape during the brewing process. Rinse the filter with a good amount of water.
Folding the filter over and holding it in place, empty the Chemex. I usually pour this into my coffee mug to preheat it a bit.
Shake the Chemex a bit to settle the grounds flat. Make sure to zero out your scale for the first pour.
Pour about 100g of water evenly over the grounds and start your timer. Optional: some people like to stir gently at this point to ensure all of the grounds are saturated. I like to think I can pour evenly enough that this is not necessary.
45 seconds after you finished your first pour, begin the second pour. Slowly pour 300g of water in concentric circles, avoiding the edges of the filter. Your total weight after this pour will be 400g.
At roughly 2:30 (or when most of the water is gone from the grounds), begin pouring the final 300g of water. Use the same method as the second pour but make sure you don't pour higher than the previous maximum height already established by the second pour. Your final weight at the end of this will be 700g.
Swirl the coffee in the Chemex and serve it!