Weighing Question

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Bamagirl

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I have the KD7000 and when I make a batch of soap and it calls for something like 3.08 oz, I can never get it at 3.08. I can either get 3.05 or 3.10. I have been just going with 3.10 of whatever it is I am weighing, but got to thinking that maybe I don't need to do that with lye? I figure it is ok with water and oils. Is this amount anything to fret over? Should I try to start weighing in grams instead? I didn't really think it was an issue until I was reading another post and saw that since I make smaller batches (I've made 1.5 lbs, and 21 oz batch sizes) it might be a bigger deal than I thought. What do you think?
 

shunt2011

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I just round up with oils or round down with lye. If it says 3.08 I use 3, if it says 3.55 I go 4. Then again, I don't use the oz setting, I always use the grams with the exception of my FO/EO. But I do the same thing. Round up for oils/butter, down for lye.
 

Bamagirl

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I just round up with oils or round down with lye. If it says 3.08 I use 3, if it says 3.55 I go 4. Then again, I don't use the oz setting, I always use the grams with the exception of my FO/EO. But I do the same thing. Round up for oils/butter, down for lye.
Thanks shunt!
 

Scarekrow

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Out of curiosity, do you think that's a problem with that particular scale or is it just difficult to measure oils/lye that accurately?
 

Steve85569

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Out of curiosity, do you think that's a problem with that particular scale or is it just difficult to measure oils/lye that accurately?
Scale.
Scales have different load cell classifications ( the thingy inside the scale that does the weighing) that are each able to weigh with different accuracy. The more accurate a load cell the more costly it is.

If you want me to I can give you a dissertation on accuracy vs precision too.
Steve
 

Chefmom

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Years ago I switched all my soap making to grams. I still think of each batch in pounds and ounces...but when I print out the recipe and scale it....it's always grams. I'm slowly getting to where if you say, that weighs 220 grams I have a general idea of what that is visually...however I'm still struggling with milliliters. If you say that is 300 mil....well....I run to a converter. I just don't have a good visual of milliliters yet.
 

cmzaha

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Scarekrow

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Accuracy is correct, precision is repeating the same result consistently. At least that's what I've been lead to believe. Are you saying I used the wrong word?
 

topofmurrayhill

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I have the KD7000 and when I make a batch of soap and it calls for something like 3.08 oz, I can never get it at 3.08. I can either get 3.05 or 3.10. I have been just going with 3.10 of whatever it is I am weighing, but got to thinking that maybe I don't need to do that with lye? I figure it is ok with water and oils. Is this amount anything to fret over? Should I try to start weighing in grams instead? I didn't really think it was an issue until I was reading another post and saw that since I make smaller batches (I've made 1.5 lbs, and 21 oz batch sizes) it might be a bigger deal than I thought. What do you think?
As you know, the implications depend on how much you are weighing. The relative error of the measurement you used in your example is +/- 1.6%. Let's say the measurement is for lye.

When we do a lye discount, we aren't actually calculating the amount of leftover superfat in the soap. We can't know that without testing our oils and lye. First and foremost, we are leaving a safety margin because we probably haven't tested those things and don't know exactly what our SAP value and lye purity is.

In the example, the 1.6% uncertainty could theoretically swallow half of a 3% lye discount, though a 5% lye discount would be a safe margin.

In reality, they are probably both okay because you are leaning towards rounding down your lye and it is definitely not 100% pure, but this should give you some insight into the issues raised by your question. If you had to weigh only 1 ounce of NaOH, the relative error with your scale would be +/- 5%.
 

cmzaha

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Accuracy is correct, precision is repeating the same result consistently. At least that's what I've been lead to believe. Are you saying I used the wrong word?
Accuracy is important but worrying about a few grams will make no difference in soap. I am not saying to purposely mis-measure but soap is forgiving with small errors, depending on batch size
 

Steve85569

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Accuracy is correct, precision is repeating the same result consistently. At least that's what I've been lead to believe. Are you saying I used the wrong word?
No.
The statement you made is correct. I wouldn't try to correct it if it wasn't here. We're making soap not doing weights out to the nearest tenth of a grain. For our purposes (making soap) they may as well be the same thing.

I also spent a considerable amount of time in a lab that required very precise measurements of mass. Accuracy and precision were both tested there to maintain certifications.

The accuracy of scales needed to make a batch of soap repeatedly that has the same qualities is all we are concerned with here.

Steve
 

Susie

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When I work, everything is metric. (I'm a nurse.) When I cook or soap, Imperial is close enough. It does not require the accuracy of grams, unless it is very small amounts of something.
 

Susie

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I should not post in the middle of the night. I meant to say that I can convert from Imperial to metric on the fly most times, so whatever anyone is comfortable with (weights, not volumes), they should stick with. And there is no denying that metric is more accurate. So, really CDO (OCD but with the letters in alphabetical order as they should be) newbies should start with metric and just be correct from the start.

But, about the use of the word precision, I think it can be used here, also:

precision
See definition in Oxford Advanced Learner's Dictionary
Syllabification: pre·ci·sion
Pronunciation: /prəˈsiZHən/
Definition of precision in English:
noun

1The quality, condition, or fact of being exact and accurate:
the deal was planned and executed with military precision
MORE EXAMPLE SENTENCES
SYNONYMS
1.1 [AS MODIFIER] Marked by or adapted for accuracy and exactness:
a precision instrument
MORE EXAMPLE SENTENCES
1.2 technical Refinement in a measurement, calculation, or specification, especially as represented by the number of digits given:
this has brought an unprecedented degree of precision to the business of dating rocks
a precision of six decimal figures
Compare with accuracy.
 
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