Rake is how far the mast is swept backwards from vertical. As the wind increases you will need to rake the mast progressively more to keep the boat balanced.
Required Rake range is
Most upright measurement 7850mm (7.85m) or 25ft 8in
Most raked measurement 7650mm (7.65m) or 25ft
You can measure rake a number of ways. The most common is by measuring the distance from the top of the mast to the keel band at the stern.
Take the measurement from the underside of the contrasting band at the top of the mast to the keel band as shown.
You can generally do this by using the main halliard to pull a tape measure to the top of the mast or putting the rigged boat on its side.
The mast must be straight to measure it properly.