Net Difference is simply subtracting one value from another value.

The Percent Difference reflects the same thing as a percentage of something. You need to ask yourself, "As a percentage of what?", and use that as the basis for your calculations.

The Percent Difference is 100 times the  Net Difference  divided by whatever you are using as a basis for your calculations.

The simplest examples of this are exemplified by two built in indicators which you could use without formulas called Rate of Change & Rate of Change Percent.

The Net Difference for the rate of change is just price minus the closing price a number of bars ago given by the period.

Where x is the period which must be an integer.

Where y is x + z.

Where z is the offset. An offset of 1 would be 1 bar ago.

A 50 period rate of change can be written as follows.

C - C50

A 50 period rate of change being less than $1 can be written as follows.

C - C50 < 1

A 50 period rate of change from 1 bar ago can be written as follows.

C1 - C51

A 50 period rate of change from 3 bars ago being at least $5 can be written as follows.

C3 - C53 >= 5

The Percent Difference in going to be the Net Difference divided by a basis. In this case the basis is going to be the closing price a number of bars ago given by the period.

Where x is the period which must be an integer.

Where y is x + z.

Where z is the offset. An offset of 1 would be 1 bar ago.

A 50 period rate of change percent can be written as follows.

100 * (C / C50 - 1)

A 50 period rate of change being less than 3% can be written as follows.

100 * (C / C50 - 1) < 3

A 50 period rate of change from 1 bar ago can be written as follows.

100 * (C1 / C51 - 1)

A 50 period rate of change from 3 bars ago being at least 1% can be written as follows.

100 * (C3 / C53 - 1) >= 1