Best way is to read the Transmitter manual.

DEFINITIONS:
• Exponential adjusts the sensitivity of the servo around the neutral position. Exponential creates a true curve, not a hard climb to a certain point then a softer climb from there. Negative exponential makes the servo less responsive around center; positive exponential makes the servo significantly more responsive around center. Only exponential is available for steering and braking.
• TH-EXP offers far more than just exponential for forward: it also offers a 5-point throttle “curve” and a Variable Trace Rate (VTR) option.
• VTR: Variable Trace Rate is basically a 3-point line, where one point may be raised or lowered, forming two straight lines, and where the user can select the
point where the line breaks into two.
• The “curve” function offers 5 points along the range of the servo, and draws straight lines of response between each point. It is not a true curve, as is exponential, and there are noticeable steps in the responsiveness as each rate of response is entered.