The best way to find #1 is to:
1. Find Top Dead Center (TDC) for #1: Use a timing light or carefully rotate the engine by hand until the #1 piston is at TDC on the compression stroke. You'll need to consult a repair manual or online resource specific to your engine for details on finding TDC.
2. Observe Rotor Position: Once #1 is at TDC on the compression stroke, look at the rotor in the distributor. Whichever contact on the distributor cap the rotor is pointing to is cylinder #1.
Do not rely solely on markings on the cap. They can be worn, inaccurate, or even missing. Using the TDC method is the only reliable way to confirm the #1 cylinder location.