Step 1: Find the order.
The order of a differential equation is the highest derivative that appears in it.
Here the term \( \dfrac{\partial^3 \varphi}{\partial x^3} \) is a third order derivative, and no higher order term is present.
So the order is \( m = 3 \).
Step 2: Find the degree.
The degree is the power of the highest order derivative term, once the equation is written as a polynomial in the derivatives with no fractional or negative powers on any derivative.
The highest order term, \( \dfrac{\partial^3 \varphi}{\partial x^3} \), shows up with power 1 only; the squared term \( \left(\dfrac{\partial^2 \varphi}{\partial x^2}\right)^2 \) uses a lower order (second order) derivative, so it does not affect the degree count.
So the degree is \( n = 1 \).
Step 3: Compute \( m - n \).
\[ m - n = 3 - 1 = 2 \]
Final Answer:
The order is 3 and the degree is 1, giving a difference of 2.
\[ \boxed{m - n = 2} \]