Converting between Clock Positions, Degrees, and Metric or Imperial Measurements Using Standard Equations or Microsoft Excel

Tuesday, April 05, 2022

Posted by Jeff Browning, Author at ASNT Pulse

Scope

Pipe inspection, specifically in-line inspection (ILI) validation work, requires an understanding of how to locate and mark a part with the area where the tool data indicates an anomaly. In direct assessment of an anomaly, the location of what is found must also be determined and reported.

Depending on the ILI tool type and vendor, the circumferential location of a call may be given in a clock position or degrees (typically measured “clockwise”, looking at the direction of flow, unless otherwise specified) and may need to be converted. This article will explain the basis for conversion between clock, degrees, and physical measurement, and how Microsoft Excel® quantifies clock as a value, which is then used to formulate the desired conversions.

What is Clock?

Clock is a unit of measurement on a circle, which is evenly divided into 12 units, with each unit equaling a value of one hour. Each hour is evenly divided into 60 sub-units, with each sub-unit equaling one minute. For the discussed purpose here, a given value in clock will be equivalent to a time value on a 12-hour clock.

For a quick understanding of this, note that if you look at a clock face, 6:00 is at the bottom extent of the circle, 12:00 the top, 3:00 the right, and 9:00 the left. Twelve hours of 60 min each means there are 720 min in the 12-hour clock. This will be important to remember.

What are Degrees?

When given in degrees, a location on a circle is represented by 360 evenly divided units, usually measured from top dead center (0 in., or 12:00), or a designated reference point. In some cases, whole value degrees are sufficient. However, if a sub-unit is required, it can be designated as a decimal place value in tenths or hundredths. If exact conversions are needed when calculating between clock and degrees or physical measurement, then you should use a sub-unit value of whole angles.

What is a Physical Measurement?

An equivalent to clock and degrees can be physically measured on a pipe, or circle. A physical measurement is in relation to the full circumference, to be accurately converted to either clock or degrees.

What is a Common Conversion Value?

All three of these measuring techniques can be easily converted by calculating the common value of percentage. If a given measurement is formulated as a percentage of the full circle, then the logic of conversions starts to become apparent.

Since percentage is represented as a sub-unit of the whole number 1, we know that 0.50 = 50%.

We have now established the groundwork for making conversions. Consider the relationship of different measurement techniques in this diagram.

Quick Conversions

While calculating percentage is an excellent method for formulating conversions, there is also a need for quick calculations that are field ready. Let’s explore a few of these relationships.

Consider there are 720 min in the 12-hour clock and 360° around a circle.

360 is exactly half of 720, which means that every 2 min is equal to 1°.

Examples

Converting Clock to Degrees

6:45 is equal to (6:00 = 6 x 60 = 360 min) + 45 min = 405 min

Since every 2 min is 1°, 405 divided by 2, equals 202.5°.

Converting back from Degrees to Clock

202.5° x 2 = 405 min

This can be solved in two ways:

405 min ÷ 60 = 6 hours with a remainder of 45 min
(Use the whole number and subtract the remainder of the min e.g. (60 min x 6 hours = 360 min, 405 min – 360 min = 45 min); or

405 min ÷ 60 = 6 hours and 0.75 hours,
0.75 is 75% of 60 sub-units (minutes)
0.75 x 60 = 45
6 hours and 45 min = 6:45

Converting Clock to Physical Measurement

With a full circumference of 62.8 in, [20 in. outside diameter (O.D)]:

6:45 is equal to (6:00 = 6 x 60 = 360 min) + 45 min = 405 min
As a percentage, 405 ÷ 720 = 0.5625 (56.25%)
0.5625 x 62.8 = 35.325 in.

You can now measure 35.325 in. in the clockwise direction from top dead center, looking direction of flow, to find the clock position 6:45.

Converting Physical Measurement Back to Clock

You have measured from top dead center, clockwise looking direction of flow, 35.325” on a 20” diameter pipe:

35.325 in. ÷ 62.8 in. = 0.5625 (56.25%)
0.5625 x 720 min = 405 min

See the two ways outlined above to convert minutes to hours: minutes

Converting Using Percentage

Any conversion can be made as a percentage by dividing the measurement by the full circle value.

Clock: 405 min ÷ 720 min = 0.5625 (56.25%)
Degrees: 202.5 ° ÷ 360° = 0.5625 (56.25%)
Physical measurement: 35.325 in. ÷ 62.8 in. = 0.5625 (56.25%)

How does Microsoft Excel Quantify a Clock Value?

What is explained here will most likely apply to any spreadsheet program; however, it has not been verified on programs other than Microsoft Excel and Google Sheets®. Google Sheets may be limited when it comes to writing formulas based on this content.

Microsoft Excel equates a clock value based on the 24-hour clock.

The 24-hour clock equals the whole number of 1.00. As such, the 12-hour clock is 50% of 1.00, or 0.50.

Establishing that a 12-hour clock value will be 0.5 or less, we can do quick calculations:

one-half of the 12-hour clock is 6:00, 0.50 × 0.50 = 0.25, so 0.25 = 6:00

Knowing this, we can write formulas to perform conversions, realizing that we must MULTIPLY or DIVIDE by 2 to get our 12-hour clock values.

Formulas for Conversion of Clock

The simplest formula, used for most basic number calculations is the “SUM” function. It is executed by typing =SUM( ) which prompts you for the first value to be used in the calculation, either a number or cell where a number value is extracted from.

Using our example values from before, let’s break this down. If:

cell B1 contains a value of 6:45,
cell C1 contains a value of 62.8 in.,
we will use the known whole circle value of 360°.

With this information, we can complete the following conversions:

Clock to Degrees

The returned value, once formatted to “number,” is 202.50, which is the value in degrees.

Clock to Physical Measurement

The returned value, once formatted to number and expanded to three decimal places, is 35.325 in.:

cell A1 contains the value for degrees calculated by the formula or manually input, and
cell A2 contains the value for physical measurement or manually input.

Degrees to Clock

The returned value (0.2813) is a percentage, when formatted to 4-digit time is 6:45.

Physical Measurement to Clock

The returned value (0.2813) is a percentage, which when formatted to 4-digit time is 6:45.

Physical Measurement to Degrees

First, formulate measurement as a percentage of the whole circumference, then multiply the product by the full circumference in degrees. This formula returned a value of 202.5°. Notice that this formula did not require multiplying or dividing by 2, since there was no conversion to or from clock.

Physical Measurement to Clock

The returned value (0.2813) is a percentage, which when formatted to 4-digit time is 6:45.

Excel Calculator

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Jeff Browning, UT NDT Level III, Precision NDT, jeffrey.browning@pndtllc.com

For more information, read ANSI/ASNT ILI-PQ-2017.