Figure 7 is a graph of the plate characteristics of a 6AS7G/6080 vacuum tube. The horizontal axis is plate to cathode voltage from 0 to 350 volts. The vertical axis is the plate current of one section from 0 to 175 milliamps. There are 8 curves on the graph each one for a different value of grid to cathode voltage. The first line is for a grid to cathode voltage of zero. It extends from 0 comma 0 to 40 comma 150. This is standard graphical notation. The first number is the X coordinate and the second number is the Y coordinate. So 40 comma 150 means a point that is at 40 volts and 150 mA. This first line is almost straight but with a little curvature. The other lines for more negative grid voltages have greater curvature as the voltage is farther from zero. The curvature is concave upwards and to the left. Note: for those who might not remember which is convex and concave, the concave side goes in like a cave. The curve for minus 20 volts goes from 35 comma 0 to 80 comma 125. The line for minus 40 volts goes from 75 comma 0 to 130 comma 125.
Minus 60 V; 100 comma 0 to 155 comma 100.
Minus 80 V; 135 comma 0 to 185 comma 100.
Minus 100 V; 165 comma 0 to 220 comma 100.
Minus 120 V; 190 comma 0 to 235 comma 50.
Minus 140 V; 215 comma 0 to 270 comma 50.
Curvature is hard to describe but the approximate center of the minus 140 volt line passes through the point 250 comma 25 rather than connecting the two end points as you would expect from a straight line. My feeling is that even for a totally blind person who is skilled at visualizing from a verbal description this description will be of little or no usefulness. At present I'm not planning on doing such a detailed description of subsequent plate characteristic graphs. If even one person finds this page useful I will put forth the labor and describe the rest. Email me if you have the need. This completes the verbal description.