for accuracy by comparing the readings of a number of thermometers exposed to atmospheric
temperature at the same time and location. Any thermometer that has a reading deviation from the other
readings by more than 0.5F is replaced.
The cup case is attached to the end of a gage tape or suitable cord.
The thermometer is then lowered to the required product level and allowed to remain at this level at least
as long as the minimum time specified in Table 3-2 of FM 10-67-1.
The thermometer is then withdrawn and read immediately with the cup sheltered below the edge of the
hatch to minimize any change of reading that may be caused by wind or atmospheric temperature. The
cup must be full when withdrawn and the product must not be spilled from the cap when taking a reading.
As quickly as accuracy will permit, the temperature is recorded to the nearest 0.5F.
When readings are taken at more than one level, all readings are added and divided by the number of
readings in order to obtain the true average temperature of the product. For example, assume a tank
had 20 feet of product in it. You would take recordings at 3 feet, 12 feet, and 21 feet, according to Table
3-1 of FM 10-67-1. Assume that readings of 82, 81, and 80F were obtained. Add these readings and
divide by three to get an average temperature.
PART C - CHECKING GAGING PROCEDURES
Accurate gage readings, temperature API gravity, and the volume of bottom sediment and water (BS&W) are
necessary to calculate the net volume of petroleum at the standard temperature of 60F. Gages are
determined through specified gaging hatches in tanks, ships, barges, tank cars, and tank trucks. There are
two basic types of procedures for obtaining gages: innage and outage. Normally, outage gage is used for
vessels and railcars, and innage gage is used for storage tanks. Bulk petroleum products are often handled
many times before they are used. Throughout this handling, they must be rigidly accounted for, and accurate
quantity records must be maintained at all times. For accountability purposes, the products must be gaged
periodically to determine the quantity of products on hand, verify quantities received or issued, detect leaks
or unauthorized withdrawals, determine presence and amount of BS&W, and determine the terminal capacity
for receiving shipments. Accounting for all receipts, issues, transfers, and operational gains and losses of
bulk petroleum products is a major responsibility of the terminal accountable officer.
Gaging Terms. The following gaging terms are used:
Innage. The depth (height or volume) of product in a tank measured or gaged from the surface of the
product to the tank bottom.
Outage (Ullage). A measurement of the free space above the surface of the product extending to the
Reference Mark. A horizontal line put in the rim of the gaging hatch representing a fixed point from
which measurements are made.
Datum Plate. A level metal plate at the tank bottom and directly under the reference mark. This plate
provides a smooth, level surface for the innage bob to rest upon.
Reference Height. The distance from the reference mark to the tank bottom or datum plate. After the
reference height is established, it is stenciled in a conspicuous place adjacent to the gaging hatch.
Innage Tape and Bob. A graduated, metallic tape and pointed bob used to determine the amount of
innage in a bulk storage tank.
Outage Tape and Bob. A graduated, metallic tape and flat bob used to determine the amount of ullage
in a bulk storage tank.
Product-Indicating Paste. A chemical paste used in measuring the amount of liquid petroleum in a
storage tank. It will change color when it comes in contact with a petroleum product.
Water-Indicating Paste. A chemical paste used to differentiate between liquid petroleum product and
water. The paste changes color when it comes in contact with water, but is not affected by petroleum
Tape Cut. The line made on the tape measuring scale by the product being measured.
Bob Cut. The line made on the bob by the BS&W being measured.
Opening Gage. A gage of a product taken before delivery, issue, or receipt of a product.
Closing Gage. A gage of product taken after delivery, issue, or receipt of a product.