Abstract: An arrangement for the attachment of means for the detection of revolutions per minute, etc., comprises a rotary member to be mounted concentrically around a hub of a wheel, said member having a single or, a plurality of, magnet pieces arranged concentrically therein and a plurality of mount openings formed concentrically therein to permit it to be attached to the spokes of a different wheel, and a detector with a built-in magnetic flux sensor mechanism which operates when it enters a magnetic field generated by said rotary member, said detector being equipped with an adjuster mechanism which is clamped onto said hub to hold said sensor mechanism within said magnetic field.

Abstract: An apparatus for measuring velocity of a bullet is shown. A portable clamping device securely holds the barrel of a gun in position during firing. A bullet fired from the gun is projected through two openings located a predetermined distance apart from the end of the gun barrel. The bullet passing through the first opening activates a timing circuit to start current flow through a measuring device. The bullet passing through the second opening stops the current flow through the measuring device. The measuring devices gives an output indication that is indirectly proportionate to velocity of the bullet with units indicating the speed of the bullet. The measuring device may be a ballistic meter with no return springs on a meter movement to remain in its maximum position after measuring current flow therethrough.