EXAMPLES OF PRECISION & TRUENESS
I remember learning the difference between accuracy and precision in high school science class (maybe Chemistry?), but I clearly didn’t carry that knowledge around for the following twenty years of my life. I’ve been using those words both interchangeably and improperly this whole time. In doing experiments that deal directly with these two concepts as well as a third counterpart of theirs (trueness) I completely neglected to use these terms. Instead, I made up phrases that described what I thought I was looking for. Luckily, I did a little digging and it turns out there were already words for exactly what I was doing—and they are:
Accuracy, and Precision & Trueness.
Do you know what these words mean, for real? I mean, could you define them to a group of unfamiliar people? Some of you likely can, but I’d wager that more than 75% of our bar population hasn’t the foggiest idea. I was one of those people just a few months ago, and I come bearing great news. These concepts are super cool, and deal heavily with what we do every day. I’m glad that I’m familiar with the terms, now. So glad, in fact, that the remainder of this article will be about what they are and why they’re important to me.
Accuracy: the extent to which a given measurement agrees with the standard value for that measurement.
· ie. If you aim to hit the bullseye, and your dart hits the bullseye, your efforts are accurate.
· I take this to mean that if one’s effort is accurate then one is correct.
Precision: the extent to which a given set of measurements of the same sample agree with their mean.
· ie. If you aim to hit the bullseye, and each of your darts hits the same spot on the board (whether the target or not), your efforts are precise.
· I take this to mean that if one’s efforts are precise then one is consistent, whether correct or not.
Trueness: the extent to which the average of a given set of measurements agrees with the standard value for that measurement.
· ie. If you aim to hit the bullseye, and each of your darts lands in the farthest four corners of the board, your efforts are true.
· I take this to mean that if one’s efforts are true then one is correct, whether precise or not.
Accuracy refers to whether or not a single value is on target, while precision and trueness describe how accurate a group of values are. Courtesy of Wikipedia, the images below detail low accuracy as follows:
But what in the world does this have to do with us? Jiggers. Free pours. Drinks. The things of which we produce hundreds weekly for thirsty guests of our restaurants. We want our drinks to be consistent from instance to instance of the same drink. We would ideally like for each Margarita we make to be roughly (or maybe even exactly) the same drink each time. Your free-pour is as good as you can make it given the time of day, mood you’re in, music playing, and any amount of other things on your mind gunking up your internal clock. I have nothing against the free-pour necessarily, but I also don’t think it fits well into this exploration. The consistency of our drinks from instance to instance has to do with a variety of factors, but the one I’m most interested in is the measurement equipment we use.
The jigger! Everyone has their preference when it comes to this argument-starting tool that many find necessary, but few agree about which one(s) to use. Well, I was tired of having sensible arguments with cohorts about the effectiveness of each different style of jigger. There has to be a clear winner, at least in terms of pure measurement power, so here are the questions I asked on the way in:
1. Do the lines on the jiggers accurately represent the desired volumes? Is the 1oz line actually showing an ounce? (accuracy)
2. How great would the difference between twelve pours from the same line be from one another? Could the 1oz line pour the same amount each time? (precision)
3. Would the average of the twelve pours from each line equal out to the volume the line purports to hold? (trueness)
On a .01g accurate scale, I placed each jigger tested and meticulously filled each line and side of the jiggers with water (no higher or lower than the line or the cup) and recorded their weight, which translates directly to milliliters, and could then be converted to ounces for my viewing pleasure. This was compared to the desired volume and that would represent the accuracy of the varying measurements on the jigger.
I then poured twelve pours from each of the markings on the jigger (so twelve in a row of .25oz, twelve of .5oz, twelve of .75oz, etc.) and recorded each of them in .01g accuracy in order to get milliliter figures for each individual pour. I took the difference between the highest and lowest pours for each target and compared that number to the target in order to find its precision, and then averaged the pours together to find the trueness of each target.
I performed these rituals for each line on each jigger tested, and eventually realized I needed to make an excel sheet of equations for this, as each set of jigger data were taking nearly twelve hours to compile and post. Due to the laborious nature of this I’ve only tested four jiggers so far, but now that the equation sheet is complete, I can re-post better organized results and test tons more jiggers!
I’ve used a gaggle of jiggers over the years, but the two most frequently used were Cocktail Kingdom’s Leopold jigger and Japanese jigger Duo. The Leopold jigger has the advantage of being an all-in-one tool, but the vast downfall of having a wide bowl. We use graduated cylinders rather than beakers to measure specific volumes, right? The shapes of the jiggers alone should be a clear indicator that the Japanese Duo will win in an overall precision battle, but do the lines on both jiggers actually read the volumes which they purport? In other words, are they even accurate to begin with? Results have been and will continue to be posted right here.
The conclusions I’ve come to are all in line with common sense, for the most part. Wider bowls are less precise, and each jigger has different starting points— by which I mean to say that some jiggers are marked incorrectly. The main conclusion to be drawn from all of this is that all jiggers I’ve come across do what they’re supposed to do. They measure booze and ensure some degree of consistency. Precise jiggers will make the same drink each time, true jiggers will make the right drink each time, and accurate jiggers will make a proper recipe drink each time. Ideally, we have all three of those qualities in one set of jiggers.
I know what I like to use, and I know why.
Knowledge is power! Can you defend your choices?
p.s. If you’d like to see a specific jigger type tested and posted in the same fashion as the others on my site, simply email me at itsme@donnyclutterbuck.com and I’ll try my best to do it! Onward and upward.