Elasticity of Supply
In the case of linear expressions, a supply curve in its simplest form would be:
or
where P denotes the price, QS denotes the quantity, and c and d are positive constants. Continuing with the maple syrup example, if the price of maple syrup increases by $1 per litre (i.e., ΔP = 1), then the quantity supplied will increase by 
. Therefore, the ratio 
is equal to 
.
Now we can look more closely at the price elasticity of supply:
Notice:
If c = 0, then the supply curve goes through the origin and the price elasticity of supply is equal to one.
If c > 0, then the supply curve intersects along the P-axis and the price elasticity of supply is greater than one (elastic supply).
If c < 0, then the supply curve intersects along the QS-axis and the price elasticity of supply is less than one (inelastic supply).
If c ≠ 0, as we move along the supply curve c and d remain constant but QS varies. Therefore the price elasticity of supply varies as we move along a linear supply curve that does not pass through the origin.