So you want to level your bed after changing a nozzle or setting up to bed level a new machine. There are many different methods to pre level your bed to begin your fine tuning but this appears to be the quickest. Either print a couple these off on a pre-levelled machine or before you change your old nozzle. place the blocks either side of the bed, on the 45 mm side and adjust the bed down or up using your corner wheels so that it has a slipfit between the underside of the bed and the printer body. if done right you now have a virtually level bed to start your fine tuning and plenty of spring adjustment on your corner wheels. Test the blocks before using to see how dimensionally accurate they are, if @ .02mm of each other size they are good to go.

For your Gantry you can check to see if it is level using the larger blocks (on Ender 3) and adjust the gantry if needed. Again check with Vernier or Micrometer to check accuracy

Creality

Ender-3 S1

No

No

10%

Do check the block size in relation to each other and make sure that you print on a machine that has had esteps and flow rate calibrated.

Having tried the pressing bed down and bottoming springs and other methods this does allow some form of accuracy that does not depend on experience