Definition
In weight and balance calculations, a station or arm measured in inches aft (rearward) of the reference datum, expressed as a positive number. Distances forward of the datum are expressed as negative inches.
Plain English
A measurement, in inches, of how far behind the airplane's chosen starting point an item or station sits. Anything behind the starting line is recorded as a positive number; anything in front of it is recorded as a negative number.
Context Anchor
Seen in aircraft weight and balance data when listing the location of seats, fuel, baggage, or equipment relative to the datum.
Derivation
The word 'positive' here is used in its mathematical sense — a number greater than zero — not in the everyday sense of 'good' or 'definite.' It simply marks direction: aft of the datum is counted as plus, forward of the datum as minus.
Why Pilots Care
Correct use of positive inches prevents sign errors that would misplace the calculated center of gravity.
Analogy
Think of the datum like the zero mark on a ruler. Measurements on one side are treated as plus numbers, so they are positive inches.
Intuition Check
Positive does not mean “good” or “safe” here. It means the distance is entered as a plus value from the aircraft’s reference point.
Example Sentence 1
The baggage compartment sits at +95 inches, so its arm is entered as a positive value in the weight and balance worksheet.
Example Sentence 2
Adding the positive inches values for each item gave the total moment used to find the CG location.