See Figure 
on p.
The orbit parameters are displayed in a box at the upper left of the initial
screen; initial values are read in from the ground.par parameter file.
To change one of these parameters move the highlighting bar until it
highlights the parameter that is to be changed, then press the Enter
key. The new value of the parameter can now be typed in, after which the Enter key must be pressed again. Movement of the blue highlighting bar is
acheived through the 
and 
cursor control
keys on the keypad.
The semi-major axis (a) is set initially to a default value of 46812.9
kilometers, corresponding to an orbital period of 28 hours. Ground will
accept any value for the semi-major axis, however, it will verify that the
value is acceptable. If it is not (if the semi-major axis and eccentricity are
such that the perigee distance is less than the radius of the earth, for
example), the computer will notify the user with a beep and an error message.
Ground will verify that the eccentricity is within the acceptable
range from 0 to 1, and that the inclination (i), right ascension of
the ascending node (
), and argument of perigee (
) are
within the acceptable range from 0 to 360 degrees. The final orbital parameter
used by ground is the mean anomaly (M) at the epoch specifed in
the ground.par file.