By a "lightning flash" on the axis, and possibly a shaded band in the graph area at right angles to the missing part of the scale.
the temperature where Fahrenheit and Celsius scale show the same numeric value is - 40
Most graphs use two scales: a horizontal scale and a vertical scale. What is on the scales depends on what the graph is to be used for. For example: the vertical scale could show distance travelled, while the horizontal scale could show the time.
I can't show a picture, but the Eb scale (I assume you mean Eb major) is Eb F G Ab Bb C D. If you specify an instrument I could show a picture.
scale
Distance.