What do you think the numbers should be? For sure you can't fake or mistake 700c. If it's an Atlantis 2, it's old. The newer ones have the newer decals and no '2'. If it's 700c and old, the smallest it could possibly be is a 58. If it's a 58 it would be 58cm center to top and darn close to 56cm center to center. The standover seems spot on for a 58. A 58 should have more like a 58.5cm effective top tube, center to center, so that's the one discrepancy. I'd bet a dollar that it's an unreliable measurer, and that it's a 58.
How much do they want for it? Do you have a link?
Bill Lindsay
El Cerrito, CA