The "Kilo" of Butter

Many years ago, in a small town outside of Israel, people lived quite harmoniously. The town had a Jewish baker, a Jewish dairyman, and so on. When the baker needed butter, which was often the case, he would go to the dairyman and purchase a kilogram block.
Once, when he purchased his usual measure of butter, he was struck that it seemed to be quite a bit lighter than a full kilo. The baker was very practiced at weighing amounts by feel since he needed to put the same amount of flour and water to produce equal breads of consistent quality every time he baked. The baker figured it was a fluke, however, and waited for his next purchase to see if the measure would be off again. On the following occasion, he was sure that he was being cheated. By the third time, the baker couldn’t control his anger and confronted the dairyman.
He accused, “I am paying you for a kilogram so why are you selling me much less? Maybe your scale is off.”
“This stick of butter is a kilo!” replied the indignant dairy seller. “If you think it’s less, then take me to a din Torah.”
Since the baker had plans to travel that very day to a nearby city where he would have access to a very accurate scale, he took the butter along and weighed it. What he saw infuriated him. The butter weighed precisely 800 grams.
The baker didn’t waste a moment. He hurried home and summoned the dairyman to a din Torah.
In front of the dayanim the baker intoned, “I weighed this butter on the accurate scale in the city. Although he claims it’s a kilo, it’s actually 800 grams.”
To the surprise of all, the dairy seller still denied it. “I will rush to bring the counterweight for my scales and your honors can see for yourselves if I perpetrate an injustice…”
When he reentered the court he held a loaf of bread in his hand. “I purchase this bread from our friend here every day. As everyone here knows, he claims it’s a kilogram loaf. If you place my butter against this bread on the scale you will see that the two are exactly even!”
The baker’s face turned beet red with embarrassment. How could he present a claim against the dairyman, when his “kilo loaf” weighed precisely 800 grams?