 Welcome to this learning object, stain measurement and calculating angle of impact. The process of measuring a blood stain and determining its angle of impact uses trigonometry's sine function. Because a mathematical relationship exists between the width and length of an elliptically shaped blood stain, it is possible to calculate the angle of the impact for the original drop of blood. If a stain is well formed, we can accurately measure the width and length of the stain by simply dividing the stain along its major and minor axis. Because the opposite halves would generally be equal to each other, this calculation establishes the angle of impact. Blood drops that are projected onto an object form ellipses when they impact the object at an angle that is less than 90 degrees. Directionality is easy to determine here, it is from right to left. If the angle of impact is 90 degrees, then the blood drop is in the shape of a circle, not an ellipse. Directionality is not always easily determined with near circular stains. In the case of the stains shown, directionality can be determined by the visible scalping, which is from right to left. Under ideal circumstances of velocity, impact angle and target surface, a drop of blood on impact would create a stain that was perfectly uniform oval shape. Ideal circumstances rarely, if ever exist, particularly in actual casework. The distortion created in response to the landscape of the target surface will prevent the stain from being a perfect oval. If the volume of the drop of blood is great enough, the blood that has not been stabilized by deposition on the surface will continue along the path of travel, creating even more deformation from the ideal elliptical stain. All of this distortion is the result of causes other than the angle of impact. For that reason, any deformation at the terminal edge of a stain must be negated when the length of the stain is measured for impact angle determination. To eliminate the distortion from the terminal edge and form an ellipse, we must measure the distance from the center of the widest point to the leading edge of the stain. This value is then doubled to arrive at the overall length of the undistorted stain. To calculate the angle of impact, the first step is to fit an ellipse to the oval shape of the stain. The ellipse must be divided along the major or minor axis. To do this, we draw a line for the length through the middle of the stain from the leading edge to the terminal edge, creating the major axis line. We determine the widest part of the stain by drawing a line to show the width of the stain, creating a minor axis. To form the ellipse, we must measure the distance from the center of the widest point, the minor axis, of the stain back toward the leading edge of the stain. This value is then doubled to arrive at the overall length of the undistorted stain. The two halves wouldn't be approximately equal to each other. The device used for measuring stains depends on the analyst. Some analysts prefer a loop with a built-in scale, while others use calipers or metric rulers. In this example, we will use a metric ruler. The major axis has been completed, and we have determined that one side of the minor axis is 1.5 millimeters. We arrived at this by measuring the distance from the center of the widest point, the minor axis, to the leading edge point of the stain. Now we double the 1.5 millimeters to make 3 millimeters, which eliminates the distortion and creates an ellipse. We now fit an ellipse to the oval shape of the stain. The width of the ellipse of the stain is 3 millimeters. Keep in mind that you must never include any portion of the satellite, scallop, or spine that may be present in the stain. Including that in the measurement would alter the overall length to width ratio and change the calculated impact angle. You need to envision a perfect ellipse superimposed on the stain. Now it's time to determine the width of the stain. Using a metric ruler, we determined that the width of the stain at its widest point is 1 millimeter, and the length of the stain is 3 millimeters. With this information, we can determine the angle of impact using the formula that states the sine of an angle equals the width divided by the length. We can calculate the angle by using either a scientific calculator or a trigonometric table. Next, we will use a scientific calculator to determine the angle of impact. The formula, as previously mentioned, is the sine of the angle equals the width divided by the length. The calculator must have the sine and inverse functions. After you turn on the calculator, enter the width of 1 millimeter and then divide that by 3 millimeters the length. This will equal 0.33 millimeters, which is the sine of the angle. Push the inverse button, followed by the sine button, which will then give you the angle of the impact, 19.5 degrees. It is that simple, but you must use a scientific calculator with the functions listed above to make it this easy. Now, we will use the trigonometric table to determine the angle of impact. Use the formula previously mentioned. The sine of the angle equals the width divided by the length. On your calculator, enter the width of 1 millimeter and then divide that by 3 millimeters the length. This will equal 0.33 millimeters, which is the sine of the angle. Now, go to the trigonometric table and find 0.33, which is between the 19 and 20 degree angle of impact. This is how to measure stands and calculate the angle of impact using a trigonometric table. We have demonstrated how to measure and calculate the angle of impact of an acute angle stain. Acute angle stains are elongated and elliptical in shape. Now, we will demonstrate how to measure and calculate the angle of a more circular shaped stain. If the angle of impact is 90 degrees, then the blood drop is in the shape of a circle, not an ellipse. As stated earlier, directionality is not always easily determined with near circular stains. Under ideal circumstances of velocity, impact angle and target surface, a drop of blood on impact would create a stain that was perfectly uniform oval shape. The distortion created in response to the landscape of the target surface will prevent the stain from being a perfect oval. Usually, to eliminate the distortion from the terminal edge and to form an ellipse, we measure the distance from the center of the widest point to the leading edge of the stain. In this near circular stain, we can see there is very little distortion, which results in little, if any, terminal edge being present. To calculate the angle of impact, the first step is to fit an ellipse to the oval shape of the stain. Forming an ellipse on this near circular stain is next to impossible because there is very little distortion. The ellipse must be divided along the major or minor axis. To do this, we draw a line for the length through the middle of the stain from the leading edge to the terminal edge, creating the major axis. We determine the widest part of the stain by drawing a line to show the width of the stain, creating a minor axis. To form the ellipse, we must measure the distance from the center of the widest point, the minor axis, of the stain back toward the leading edge of the stain. This value is then doubled to arrive at the overall length of the undistorted stain. The two halves would be approximately equal to each other. To measure a blood stain, some analysts prefer a loop with a built-in scale, while others choose to use calipers or metric rulers. In this example, we will use a metric ruler. The major axis has been completed and we have determined that one side of the minor axis is 0.75 millimeters. We arrived at this by measuring the distance from the center of the widest point, the minor axis, to the leading edge point of the stain. Now we double the 0.75 millimeters to make 1.5 millimeters, which eliminates the distortion and creates an ellipse. We have now determined the length of the near-circular-shaped stain. The width of the ellipse of the stain is 1.5 millimeters. Remember, you must never include any portion of the satellite, scallop, or spine that may be present in the stain. In the stain shown here, there is scalloping, which should not be included. Including that in the measurement would alter the overall length-to-width ratio and change the calculated impact angle. Now it's time to determine the width of the stain. The device we used here to measure the minor axis width is a metric ruler. The stain width is 1.4 millimeters and the stain length is 1.5 millimeters. With this information, we can now determine the angle of impact. To do so, we must use this formula. The sine of the angle equals the width divided by the length. We can calculate the angle of impact by either using a scientific calculator or trigonometric chart. Next, we will use a scientific calculator to determine the angle of impact. The formula, as previously mentioned, is the sine of the angle equals the width divided by the length. The calculator must have the sine and inverse functions. Turn on the calculator. Enter the width of 1.4 millimeters and then divide that number by 1.5 millimeters the length. This will equal 0.93 millimeters, which is the sine of the angle. Push the inverse button, followed by the sine button, which will then give you the angle of impact of 68.9 degrees. It is that simple, but you must use a scientific calculator with these functions to make it this easy. Finally, let's use the trigonometric table instead of a calculator to determine the angle of impact. Use the formula previously mentioned, which is the sine of the angle equals the width divided by the length. On your calculator, enter the width of 1.4 millimeters and then divide that number by 1.5 millimeters the length. This will equal 0.93 millimeters, which is the sine of the angle. Now, go to the trigonometric table and find 0.93, which is a 69 degree angle of impact. You have now seen how to measure stands and calculate the angle of impact of different shaped stands. Congratulations, you have completed this activity. Stain measurement and calculating angle of impact.