What a profile is
Every gate in Human Design has six lines, each a slice of the zodiac 56′15″ wide. Your profile takes the line of your Sun at birth and the line of your Sun at the Design moment, 88° earlier, and writes them as two numbers: a 5/1, for example, has the conscious Sun in a fifth line and the Design Sun in a first. The first number is read as the role you know you play, the second as the one others see. Each line divides further, into six colors and then six tones, and those set the four arrows of the Variable.
The six lines
The lines go from the personal to the social. The first, the Investigator, wants a secure foundation of knowledge. The second, the Hermit, has natural talents others notice and call out. The third, the Martyr, learns by trial and error. The fourth, the Opportunist, works through a network of friends. The fifth, the Heretic, carries others' projections and is expected to solve things. The sixth, the Role Model, lives in three phases and becomes an example to others later in life.
Why only twelve, and why six are rare
The two Suns are always 88° apart, which is about 93.9 lines. That fixes how the two numbers line up: most of the time the Design Sun's line sits two lines past the Personality Sun's (so 1/3, 2/4, 3/5, 4/6, 5/1, 6/2), and only near the edge of a line does it sit three lines past (1/4, 2/5, 3/6, 4/1, 5/2, 6/3). Measured on 10,000 birth moments spread evenly over 1950 to 2009, the first six take 14 to 15% of charts each and the second six only 2.1 to 2.5% each. No other pairings can happen.
Profiles and the cross
The profile also sets the angle of the incarnation cross, the chart's largest theme. Profiles 1/3 to 4/6 have Right Angle crosses, read as a personal destiny; the 4/1 alone has a Juxtaposition cross, a fixed path; and 5/1 to 6/3 have Left Angle crosses, read as a destiny lived through others. The free Human Design chart calculator gives your profile and cross with the gates of both Suns and Earths, and the guide to the incarnation cross lists all 192 crosses by gate.