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Thread: Understanding accuracy percentages of test kits and/or equipment

  1. #1
    Sashimi

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    Understanding accuracy percentages of test kits and/or equipment

    I remember seeing Boomer explain this once before but I'm not sure where I ran across it. IIRC, it's not as simple as it seems.
    If my test kit has an "Accuracy 4% 0.04 ppm (mg/L) of reading 0.04 ppm (mg/L)" does that mean at a reading of .05 the accuracy is +/- .002 ppm or the reading could be some where between .09-.01 ppm?

    I think I remember something about the accuracy changes proportionally to the reading.
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    hmmm... I thought accuracy was constant when within the range of the test kit. I'll be tagging along to see if (when) I'm totally wrong.
    -Stacey
    30 gallon nem tank /60 gallon softie tank/75 mixed reef /5 gallon pico (work tank)
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    Copepod

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    Which is more important accuracy or consistency??

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    depends on how inaccurate the consistency is?
    i prefer consistent, but for new(er) folks, accuracy tends to be more important. i can read my tank a bit now without having to test. when i couldn't, i needed accuracy to diagnose... now i want consistency since i have tank indicators. tank tells me somethings off, i just need to know which of my numbers test wrong (compared to my consistent results), not how accurate the number really is..
    -Stacey
    30 gallon nem tank /60 gallon softie tank/75 mixed reef /5 gallon pico (work tank)
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    Copepod

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    That is my thinking also.
    My corals can indicate when something's not right.

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    Oldsaint

    That does not look like it is written right. Here is a known accuracy for a meter


    Iodine 0.1 mg/L 5% of reading

    It means you have a reading, where you take 0.1 mg / l and 5% of the reading.

    If the reading is 10 ppm then;

    10 mg / l - 0.1 mg/ l = 9.9 mg/l

    9.9 x 5 % = 0.495 gives

    9.405

    So, at a reading of 10 ppm they are guaranteeing the actual level is somewhere between 9.405 - 10.405 ppm, you do not know where. So, round that off and you have an Accuracy @ 10 ppm of 0.4 mg/ l.

    If you were to work out 3 mg/ l

    3 - 0.1 = 2.9

    2.9 x 5% = 0.145 gives

    2.755

    Accuracy @ 3 mg/ l 0.245 mg/ l or ~ 0.2 mg/l

    So, your actual level is somewhere between 2.8 - 3.2 mg/ l, you do not know where.
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    Sashimi

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    It's not written correctly. I see that now. Not sure where I ran across it but it had me confused.

    I tested a fellow reefer's tank with a HI-97713. He used his 713 checker a few days later and got a higher reading. I went to see if the readings were within range and got that some where.

    I have both meters with me and looking through I see that both have the same accuracy 0.04 (mg/L) 4% of reading(mg/L) and see how the math works.

    Thank you very much.
    Wisdom and knowledge is your's to fish.

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  8. #8
    Copepod

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    Quote Originally Posted by Boomer View Post
    Oldsaint

    That does not look like it is written right. Here is a known accuracy for a meter


    Iodine 0.1 mg/L 5% of reading

    It means you have a reading, where you take 0.1 mg / l and 5% of the reading.

    If the reading is 10 ppm then;

    10 mg / l - 0.1 mg/ l = 9.9 mg/l

    9.9 x 5 % = 0.495 gives

    9.405

    So, at a reading of 10 ppm they are guaranteeing the actual level is somewhere between 9.405 - 10.405 ppm, you do not know where. So, round that off and you have an Accuracy @ 10 ppm of 0.4 mg/ l.

    If you were to work out 3 mg/ l

    3 - 0.1 = 2.9

    2.9 x 5% = 0.145 gives

    2.755

    Accuracy @ 3 mg/ l 0.245 mg/ l or ~ 0.2 mg/l

    So, your actual level is somewhere between 2.8 - 3.2 mg/ l, you do not know where.
    Wow to much math

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