Measurement is in kilograms instead of pounds

Question edited for a lot more clarity.

Here is the manual

Tanita BC-420MA Instruction Manual - ManualsLib

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Summary of Contents for Tanita BC-420MA. Page 1 BODY COMPOSITION ANALYZER BC-420MA Instruction manual REMOTE DISPLAY VERSION COLUMN MOUNTED VERSION Please read ...

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Taylor digital scale, Model # 5721F
Taylor electronic scales are designed to measure your personal weight, as well as your body fat and water weight. Your scale will measure in either pounds or kilograms, indicating your weight to the nearest ounce or gram. You can use the scale as a weight only device or you can take advantage of its bells and whistles by completing the programming process. The scale will store data for up to 10 users. Setup takes only a few minutes.
Set the scale to your choice of kilograms or pounds. The default measurement for the scale is pounds/inches. To change this setting, change the switch on the underside of the scale to kilograms.

SOURCE:Scales show weight in kg. How to get them to show lbs.
Body Fat Monitor/Scales: TBF-611, TBF-612, TBF-621, TBF-622, BF-541, TBF-560, TBF-572. UltimateScales: 2000, 2001, 2001T. BF-662, BF-555, BF-556, BF-558, BF-559, BF-625, BF-626.
Press the Set and Up Arrow buttons at the same time. Release the buttons, the display will flash. Press the Arrow button to cycle through each weight mode until just the mode that you require is displayed. Then press Set. The display screen will flash to confirm your selection and store in memory.
Note: If weight mode is set to pounds or stone-pounds, the height programming mode will be automatically set to feet and inches. Similarly, if kilograms is selected, height will be automatically set to centimeters.

Mine too! What the heck?

Since your problem started with a battery change, I am going to assume that method 1 is most likely going to fix your problem...Good luck!



Method 1
Press the Set and Up Arrow buttons at the same time. Release the buttons, the display will flash. Press the Arrow button to cycle through each weight mode until just the mode that you require is displayed. Then press Set. The display screen will flash to confirm your selection and store in memory.
Note: If weight mode is set to pounds or stone-pounds, the height programming mode will be automatically set to feet and inches. Similarly, if kilograms is selected, height will be automatically set to centimeters.
Method 2
Body Fat Monitor/Scales: BF-542, TBF-551, TBF-521, TBF-531, BF-681, BF-682, BF-679, BF-680, BF-578, all Ironman products, and all InnerScan products.
Select the preferred weight mode by using switch on the back of the measuring platform.
Note: If weight mode is set to pounds or stone-pounds, the height programming mode will be automatically set to feet and inches. Similarly, if kilograms is selected, height will be automatically set to centimeters.

Q: Why does "st-lb" or "kg" appear when taking a measurement?
A: The unit's "Weight Mode" has been set to measure your weight in units of stone-pounds (st-lb) or kilograms (kg). Tanita's Body Fat Monitors and the UltimateScales can measure weight in three different modes: lb (pounds), kg (kilograms) or st-lb (British stone-pounds). To change the setting, first find out which model you have (it should be written just above or below the display screen of the unit).
Method 1
Body Fat Monitor/Scales: TBF-611, TBF-612, TBF-621, TBF-622, BF-541, TBF-560, TBF-572. UltimateScales: 2000, 2001, 2001T. BF-662, BF-555, BF-556, BF-558, BF-559, BF-625, BF-626.
Press the Set and Up Arrow buttons at the same time. Release the buttons, the display will flash. Press the Arrow button to cycle through each weight mode until just the mode that you require is displayed. Then press Set. The display screen will flash to confirm your selection and store in memory.
Note: If weight mode is set to pounds or stone-pounds, the height programming mode will be automatically set to feet and inches. Similarly, if kilograms is selected, height will be automatically set to centimeters.
Method 2
Body Fat Monitor/Scales: BF-542, TBF-551, TBF-521, TBF-531, BF-681, BF-682, BF-679, BF-680, BF-578, all Ironman products, and all InnerScan products.
Select the preferred weight mode by using switch on the back of the measuring platform.
Note: If weight mode is set to pounds or stone-pounds, the height programming mode will be automatically set to feet and inches. Similarly, if kilograms is selected, height will be automatically set to centimeters.

Body Fat Monitor/Scales: TBF-611, TBF-612, TBF-621, TBF-622, BF-541, TBF-560, TBF-572. UltimateScales: 2000, 2001, 2001T. BF-662, BF-555, BF-556, BF-558, BF-559, BF-625, BF-626.
Press the Set and Up Arrow buttons at the same time. Release the buttons, the display will flash. Press the Arrow button to cycle through each weight mode until just the mode that you require is displayed. Then press Set. The display screen will flash to confirm your selection and store in memory.
Note: If weight mode is set to pounds or stone-pounds, the height programming mode will be automatically set to feet and inches. Similarly, if kilograms is selected, height will be automatically set to centimeters.

You didn't mention brand name or model number, so not sure about your specific case. However, on my scale, there is a switch or button near the battery compartment. It allows you to change the measurement between stones, pounds and kilograms. 

Press the Set and Up Arrow buttons at the same time. Release the buttons, the display will flash. Press the Arrow button to cycle through each weight mode until just the mode that you require is displayed. Then press Set. The display screen will flash to confirm your selection and store in memory.
Note: If weight mode is set to pounds or stone-pounds, the height programming mode will be automatically set to feet and inches. Similarly, if kilograms is selected, height will be automatically set to centimeters.

On my model, there is a button on the bottom that slides back and forth to choose the wanted setting. My scale is about 5 years old.