condition that the angle b is fixed to 75 u00b0 and the angle a has a range of possible angle value of 30 u00b0 to 60 u00b0 set with the slider s the user deletes the slider s for the angle a from the display screen 3 and then the user sets up a slider for the angle c as shown in fig7 c step s 15 in fig3 yes in this connection the user can delete the slider s from the display screen 3 by touching the area other than the slider s area and the graphic area with the touch pen p on the display screen 3 when the slider s is on the display screen 3 in this case in the process for determining the range of possible angle value shown in fig4 the angle b is fixed to 75 u00b0 step s 32 yes the number of fixed angles is one step s 33 no the angle a has the range of possible angle value with the slider s that is the angle a has slider range settings step s 34 yes under this condition the cpu 11 determines the minimum and maximum values of the range of the slider s for the angle c based on the sum of the interior angles of an n gon 180 u00b0 u00d7 n u2212 2 as follows step s 36 minimum value 180 u00b0 u00d7 n u2212 2 u2212 u03c3 fixed angle values u2212 maximum values within the set range and maximum value 180 u00b0 u00d7 n u2212 2 u2212 u03c3 fixed angle values u2212 u03c3 minimum values within the set ranges 2 specifically in fig7 b the angle b of the triangle is fixed to 75 u00b0 and.