as stated earlier , the apparatus of the invention 10 is basically a two part tool comprising a tab part 12 that is used with the tab at the end of the tape of a conventional tape measure , and a tape part 14 that is used with the tape of the conventional tape measure . in the example of the apparatus 10 to be described , both the tab part 12 and the tape part 14 are constructed of metal . this gives the two parts of the apparatus sufficient strength to be used in confirming right angles at corners of a rectangular structure constructed of metal . other embodiments of the apparatus 10 could be constructed of other materials . as shown in fig1 and 4 , the tab part 12 of the apparatus 10 includes a base 16 having a general triangular configuration with opposite top 18 and bottom 20 surfaces . the top 18 and bottom 20 surfaces are flat , parallel surfaces . the base 16 has two intersecting side surfaces 22 , 24 that are oriented at a right angle to each other . the intersecting side surfaces 22 , 24 have substantially the same length . the base also has a couple of shorter side surfaces 26 , 28 and a longer side surface 30 that extends between the shorter side surfaces . the side surfaces of the base 16 give the base its general triangular configuration . however , it is not necessary that the base 16 have the triangular configuration shown in fig1 and 4 for proper functioning of the tab part 12 . as shown in fig4 and 6 , a cylindrical hole 32 is formed in the base bottom surface 20 . the hole 32 extends upwardly through the bottom surface 20 and into the base 16 , but does not extend completely through the base . the hole 32 is located in a central area of the tab part base 16 . a cylindrical magnet 34 is positioned in the hole 32 in the base bottom surface 20 . the magnet 34 is dimensioned to occupy much of the interior volume of the hole 32 in the base . referring to fig1 , 2 , 4 and 6 , a plate 36 is secured to the tab part 16 . the plate 36 has a triangular portion 38 that extends over the base bottom surface 20 and the hole 32 in the bottom surface and secures the magnet 34 in the hole . the configuration of the plate triangular portion 38 closely follows the triangular configuration of the base bottom surface 20 . the plate 36 also has an elongate flange 40 that is oriented at a right angle to the plate triangular portion 38 . the flange 40 extends across the longer side surface 30 of the base 16 and is secured to the side surface by a pair of threaded fasteners 42 . a pair of the elongate blocks 44 , 46 are secured to the base bottom surface 20 along the intersecting side surfaces 22 , 24 of the base . each of the elongate blocks 44 , 46 has a rectangular configuration except for a notch 48 , 50 formed in a bottom surface of each block . the opposite top surface of each block 44 , 46 is positioned against the plate triangular portion 38 on the base bottom surface 20 and the blocks 44 , 46 are secured to the base bottom surface 20 by pairs of threaded fasteners 52 , 54 . the fasteners 52 , 54 and their respective blocks 44 , 46 thereby further secure the plate 36 to the tab part base 16 . the blocks 44 , 46 have flat interior surfaces 56 , 58 that oppose each other . the interior surfaces 56 , 58 define a right angle between the surfaces having an apex 60 . coplanar straight lines projected across the block interior surfaces 56 , 58 intersect at the apex point 60 shown in fig4 . referring to fig1 , 2 , 4 and 6 , a cylindrical tab post 64 projects outwardly from the base top surface 18 . as shown in fig7 , the tab post 64 is mounted for rotation on the base top surface 18 by a stub shaft 66 that extends downwardly through a hole formed in the base top surface . the stub shaft 66 extends through a smaller diameter portion of the hole to a larger diameter portion of the hole . a retaining ring 68 mounted on the stub shaft 66 in the larger internal diameter portion of the hole secures the tab post 64 to the base top surface 18 . the tab post 64 is rotatable on the base top surface 18 about a rotation axis that intersects the apex 60 of the angle formed between the block interior surfaces 56 , 58 on the bottom surface 20 of the base . referring to fig1 , 2 , 4 and 6 , the tab post 64 projects outwardly from the base top surface 18 to a top surface 70 of the post . a notch or groove 72 is formed in the post top surface . the notch 72 has an edge 74 that is positioned in a plane that intersects the axis of rotation of the tab post 64 and the apex 60 of the right angle formed by the first and second blocks 44 , 46 on the base bottom surface 20 . the notch 72 is dimensioned to receive a tape measure tab inserted in the notch . a spring biased detent 76 is provided on the tab post 64 on the opposite side of the notch 72 from the notch edge surface 74 . when a tape measure tab is inserted in the notch 72 the tab compresses the spring of the detent 76 and the spring force exerted on the detent holds the tab against the edge surface 74 and in the notch 72 . a pair of studs 78 are inserted into holes in the base top surface 18 and project outwardly from the top surface . the studs 78 are positioned equal distances from the tab post 64 and are directly above the interior surfaces 56 , 58 of the first 44 and second 46 blocks secured to the base bottom surface 20 . a pin 80 is inserted into a hole formed in the side of the tab post 64 . the pin 80 projects outwardly from the tab post parallel over the base top surface 18 . the pin 80 has a center axis that intersects the tab post 64 axis of rotation . the pin 80 projects a sufficient distance from the tab post 64 to engage with one of the pair of studs 78 when the tab post 64 is rotated in opposite directions on the tab part base 16 . thus , the pair of studs 78 limit the rotation of the tab post 64 to a 90 ° arc . the tape part 14 has a construction that , for the most part , is the same as that of the tab part 12 . therefore , the construction of the tape part 14 that is the same as the tab part 12 will not be described in detail , and the component parts of the tape part 14 that are the same as those of the tab part 12 will be labeled with the same reference numbers employed in the description of the tab part 12 with the reference numbers being followed by a prime (′). referring to fig1 , 3 , 5 and 7 , the tape part 14 also has a base 16 ′ with a general triangular configuration and flat , parallel top 18 ′ and bottom 20 ′ surfaces . the tape part base 16 ′ also has a pair of intersecting side surfaces 22 ′, 24 ′, a pair of shorter side surfaces 26 ′, 28 ′ and a longer side surface 30 ′. as shown in fig5 and 7 , a cylindrical hole 32 ′ extends into the tape part bottom surface 20 ′ and a cylindrical magnet 34 ′ is positioned in the hole . referring to fig1 , 3 , 5 and 7 , a plate 36 ′ is secured to the tape part bottom surface 20 ′ with a triangular portion 38 ′ of the plate extending over the bottom surface 20 ′ and securing the magnet 34 ′ in the hole 32 ′, and with a flange 40 ′ of the plate extending over the longer side surface 30 ′ of the base . a pair of fasteners 42 ′ secure the flange 40 ′ to the longer side surface 30 ′ of the base 16 ′. first 44 ′ and second 46 ′ elongate blocks are secured to the base bottom surface 20 ′. just as with the tab part 12 , the blocks 44 ′, 46 ′ have notches 48 ′, 50 ′ in their bottom surfaces and are secured to the tape part base 16 ′ by a pair of fasteners 52 ′, 54 ′. the blocks 44 ′, 46 ′ also function to secure the plate 36 ′ to the base bottom surface 20 ′. interior surfaces 56 ′, 58 ′ of the first 44 ′ and second 46 ′ blocks define a right angle between the surfaces . straight , coplanar lines extended across the surfaces 56 ′, 58 ′ intersect at an apex point 60 ′ shown in fig5 . referring to fig1 , 3 , 5 and 7 , the tape part 14 also includes a cylindrical tape post 64 ′ that is mounted for rotation on the top surface 18 ′ of the tape part base 16 ′. as shown in fig7 , the tape post 64 ′ has a stub shaft 66 ′ that is inserted into a hole formed in the base top surface 18 ′ and is secured in the hole by a retainer ring 68 ′. the tape post 64 ′ projects outwardly from the top surface 18 ′ of the tape part base 16 ′ to a top surface 70 ′ of the post . the tape part 14 of the apparatus differs from the tab part 12 in the construction of the top surface 70 ′ of the tape post 64 ′. the tape post top surface 70 ′ is formed with a recessed curved surface 82 . the curved surface 82 at the top of the tape post 54 ′ is dimensioned to match the cross - section curvature of the tape of a conventional tape measure . a pair of collinear indicator grooves 84 are formed in the tape post top surface 70 ′ on opposite sides of the curved surface 82 . a straight line extending through the pair of indicator grooves 84 intersects the axis of rotation of the tape post 64 ′ and the apex 60 ′ of the right angle defined by the interior surfaces 56 ′, 58 ′ of the first 44 ′ and second 46 ′ blocks on the bottom surface of the tape part base 16 ′. the method of using the apparatus 10 to confirm the right angles of the corners of a rectangular structure with a tape measure first involves positioning the tab part 12 and the tape part 14 of the apparatus over first and second diagonally opposite corners of the structure . for example , the tab part 12 of the apparatus is positioned over a first corner of the structure with the bottom surface 20 of the tab part 12 engaging over the corner and the interior surfaces 56 , 58 of the first 44 and second 46 blocks of the tab part 12 engaging against opposite sides of the corner of the structure . this positions the edge surface 74 on the tab part post 64 directly over the apex of the structure first corner . the tape part 14 is then positioned over the diagonally opposite corner of the structure with the bottom surface 20 ′ of the tape part engaging over the corner and the interior surfaces 56 ′, 58 ′ of the first 44 ′ and second 46 ′ blocks on the tape part bottom surface 20 ′ engaging against the opposite sides of the second corner of the structure . this positions the line between the indicator grooves 84 on the tape part post 64 ′ directly over the apex of the structure second corner . when the structure is constructed of metal , the magnets 34 , 34 ′ in the respective tab part 12 and tape part 14 hold them to the corners of the structure . in use with non - ferris materials , the magnets could be replaced with suction cups , clamps or other equivalent devices . the tab of the tape measure is then positioned in the notch 72 in the top surface 70 of the tab part post 64 . the detent 76 urges the tab part of the tape measure against the edge surface 74 of the notch and securely holds the tab of the tape measure in the notch 72 . the tape of the tape measure is then extended from the tape measure housing across the structure to the tape part 14 of the apparatus at the diagonally opposite second corner of the structure . the ability of the tab part post 64 to rotate assists in securing the tape measure tab in the post notch 72 as the tape measure is moved to the second corner . the tape of the tape measure is then positioned over the recessed curved surface 82 in the top of the tape part post 64 ′. a distance measurement diagonally across the rectangular structure from the first corner apex to the second corner apex is determined from observing the measurement on the tape measure tape between the indicator grooves 84 on the tape part post 64 ′. the tab part 12 and the tape part 14 are then moved to the other diagonally opposite third and fourth corners of the rectangular structure and the measurement method described above is repeated . the two diagonal distance measurements between the first and second corners and the third and fourth corners of the structure are then compared to see if they are equal and to thereby confirm the right angles at the corners of the rectangular structure . as various modifications could be made in the construction of the invention herein described and illustrated without departing from the scope of the invention , it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting . thus , the breadth and scope of the present invention should not be limited by any of the above described exemplary embodiments , but should be defined only in accordance with the following claims appended hereto and their equivalents .