  We introduce two invariants called the secondary cuspidal curvature and the
bias on $5/2$-cuspidal edges, and investigate their basic properties. While the
secondary cuspidal curvature is an analog of the cuspidal curvature of
(ordinary) cuspidal edges, there are no invariants corresponding to the bias.
We prove that the product (called the secondary product curvature) of the
secondary cuspidal curvature and the limiting normal curvature is an intrinsic
invariant. Using this intrinsity, we show that any real analytic $5/2$-cuspidal
edges with non-vanishing limiting normal curvature admits non-trivial isometric
deformations, which provide the extrinsity of various invariants.
