HOW DO YOU CALIBRATE THE SCALES ON A ROBINAR 34800...

Just remove the battery, wait 15 minutes and replace it. There is no calibration on home use scales because you would need a guaranteed calibration weight.

Are these a vintage or a digital scales? Is this for general cooking and baking or is it for accurate measuring?
General cooking doesn't need serious accuracy so unless it is seriously inaccurate I wouldn't worry too much about it.
Digital scales can be difficult to accurately calibrate without specialist equipment. For accurate measuring there are companies out there that can calibrate scales to an industrial standard for a fee.
You can check the accuracy of any scale buy using something you know the EXACT weight of. (Bag of sugar or flour). Set up the scales as normal. Add the known weight and read the scale. If it is more than a gram or two out it needs calibrating. On digital scales you might need to press the 'TARE' button before you start to Zero the display.
Most old 'mechanical' scales use a spring as the resistance to the weight you put onto the scale. You can get some adjustment but as the spring gets old it weakens and gets less accurate. Somewhere on the scale there will be an adjuster wheel. Often positioned high up on the back of the scales. *Note* mechanical scales are often not very exact so there will always be some level of inaccuracy.
Set the scales up as you would normally use them. Look at where the needle sits near the '0' mark. Turn the adjuster wheel a few turns, (counting them), in one direction. Press the weight 'Plunger' all the way down two or three times. Check where the needle has moved to. If it has moved the 'wrong' direction wind the adjuster wheel back the number of turns you counted, (the start position), then continue in that direction the same number of turns. Press the plunger down like you did the first time.
This method will show you which way to turn the adjuster and how far to get it back to where the '0' mark is.

Visit the linked site to know more.
http://www.freesolutionmanual.com/pdf/search/Calibrate-ts56-scales-instruction-manual.html

http://electronicshelponline.blogspot.com/

youtube:

How To Calibrate A Digital Scale - YouTube

? 1:07
www.youtube.com/watch?v=VRZ5FDF5IFk

Scales are supposed to show correct weigt. Who told you to "calibrate" it? Your scale is not working correctly. Return it and ask for a good scale

500ml 0f water is exactly 500g, measure that volume and put it in freezer bag and use as calibration weight, or if you have friend with scales - borrow from him scale weights.

if you use water - accuracy of the scale will not be absolute, it may vary few g either way.

another way - go to shop and buy 500g block of butter - put it on the scale in the shop - remove or add as you need till you have exact 500g, shop scales are accurate on that weight within 2g

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Take a ten pound bag of sugar and calibrate the scale to read 10 pounds.

It's important to find the model number to be able to find the correct manual. Below is a link to FAQ's about Taylor body fat scales.
If you do a google search for "taylor body fat scale" you will see a list of a few models. Examine each to see if one of them is the same as yours.
Taylor USA FAQs Scales

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There are different digital scales available for the home, or in your business (like your kitchen scale, bathroom scale, weight scale or food scale), but you have to calibrate them first before you can use them. There are different brands of digital scales like Primo and Tanita, and each of these brands has different instructions on how to operate them for calibration.

Infor from: OBD diagnostic tool one stop supplier

i needs manuals of calibration of the scale salter model 6055