Abstract: An educational apparatus used for the teaching of mathematical operations that use fractions. A triangular shaped ruler prism has three different side surfaces that are joined together at three common edges with four different numerical value measuring fractional scales on each side surface and a whole unit scale of which all other scales are a fractional part thereof. All scales have the same length as the whole unit scale. Preferably on each prism side there are two different fractional measuring scales adjacent and aligned with each other in a straight line at one of the common joined prism edges. Fractional scale measuring units that have been used include; the whole unit, half units, thirds, fourths, fifths, sixths, sevenths, eights, ninths, tenths, elevenths and twelfths units. By stated procedures employing marking on a writing surface, fractions may be represented by lengths and added or subtracted from each other as well as mixed numbers with fractions.