A method is disclosed for a portable peripheral memory storage device. The disk holder and the braking disk are mounted so that they can move relative to each other in the radial direction to compensate for different thermal expansions. Methods for improving the fuel economy of an internal combustion engine are also provided. The projection portion securely climbs over the annular projection for its flexibility in a diametrical direction of the hole. And if particle groups having a known particle size are dispersed in a liquid to be measured and similar measurements are performed, viscosity analysis of the liquid to be measured can be performed.