Abstract: A calculator of flat design with a surface chart showing marginal scales and diagonal inner ones. The top of the calculator serves as a cover attached marginally to a case underneath. Also, the top has a diagonal slot, and is surmounted by a flat pointer which has a similar slot, and can be slid and rotated to relate to numerical values in the scales. An axial post is installed to pass through and be movable to any desired point in the slots, with means disengaging the post by finger pressure for movement away from said point.