Precision granite surface plate or alternative

Did you check yours?

Nope ! Was using it as indicated. If I were to use it for checking the crankshaft I'd start by getting a piece long enough to support the V-blocks. It's a LONG crankshaft!
Then I'd check the slab for trueness. Seems illogical to pay over $100.00 for a small piece that then would be dependant on the true-ness of your "work-bench".

from a "search":

Why granite? Is it better than steel or cast iron for precision surfaces?

The answer is 'yes' for almost every application. The advantages of granite include: No rust or corrosion, almost immune to warping, no compensating hump when nicked, longer wear life, smoother action, greater precision, virtually non-magnetic, low co-efficient of thermal expansion, and low maintenance cost.

How should my surface plate be supported? Does it need to be level?

A surface plate should be supported at 3 points, ideally located 20% of the length in from the ends of the plate. Two supports should be located 20% of the width in from the long sides, and the remaining support should be centered. Only 3 points can rest solidly on anything but a precision surface.
The plate should be supported at these points during production, and it should be supported only at these three points while in use. Attempting to support the plate at more than three points will cause the plate to receive its support from various combinations of three points, which will not be the same 3 points on which it was supported during production. This will introduce errors as the plate deflects to conform to the new support arrangement.
If the plate is properly supported, precise leveling is only necessary if your application calls for it. Leveling is not necessary to maintain the accuracy of a properly supported plate.

Yeah, it's 18" long, and for some reason a number 60 cm stuck in my head and I don't know where it came from. About 45 cm might be too short. I was going to check it and will do so soon.

Thanks for the info, my search showed that as well! haha But I think we new it already

Shoot.. 21 inches would be perfect, 18 just a bit short..... Unless I'd support it on the second journal on one side. Not by the book, but I think it would work.