Keithley 2015 THD Multimeter vs. Standard Bench Digital Multimeter: A Practical Comparison

The Comparison You're Actually Stuck On

If you've searched for a Keithley bench digital multimeter recently, you've probably hit the same fork: the Keithley 2015 THD multimeter versus a standard benchtop DMM. Do you really need the THD option, or is it a feature you'll touch once and forget?

Take it from someone who made both mistakes: I've spent eight years selecting test equipment for an electronics development lab, and I've personally made — and documented — four significant buying mistakes, totaling roughly $9,000 in wasted budget. The first mistake was buying a standard DMM when I needed distortion measurements. The second was over-correcting and buying the 2015 for a job that only needed clean DC readings.

Here's the comparison I wish I'd had before spending that money. Four dimensions: measurement capability, real cost, usability and training, and application fit. I'll give you a straight answer at the end of each one.

Dimension 1: Measurement Capability — What Each Meter Really Does

The Keithley 2015 is, at its core, a 6.5-digit multimeter. So is the Keithley 2000, along with most of the Keithley bench DMM lineup. Both measure DC and AC voltage, DC and AC current, resistance, frequency, and temperature. The difference is what happens when the signal isn't clean.

The 2015 adds total harmonic distortion (THD) and AC level measurement. It reports distortion in percent or dB, and it can break down the harmonics individually. For audio amplifier testing, power supply design, or power quality work, that capability is the difference between guessing and knowing.

A standard bench DMM — the Keithley 2000, say — gives you a clean voltage number. But if you need to account for harmonic content, or rather, if you need to measure it, you'll need an external THD analyzer. That's another box, another calibration cycle, another learning curve.

Conclusion: if your work touches distortion specs, the 2015 isn't a DMM with a bonus feature. It's two instruments in one. If your work is mostly DC, current, and resistance, you're paying for a feature set that will gather dust.

Dimension 2: The Real Cost — Which One Costs More Over a Year

Let's talk numbers. As of early 2025, the used market tends to price a Keithley 2015 around $1,300–$1,800 with a recent calibration, while a Keithley 2000 in similar condition lands around $700–$1,000. New prices through authorized distributors differ even more. That gap is the reason most people hesitate. I know it's why I did.

Now the part I didn't calculate in 2017: the cost of not having THD when you need it. I bought the standard meter, found out three months later that a project needed harmonic analysis, and rented a THD analyzer at $350 per week. Extending the rental to complete the project cost $1,200. That one rental covered more than the entire used-price gap between the two meters.

The counterintuitive part: the "cheaper" meter ended up more expensive than the 2015 within one project cycle. That's not a universal rule — it depends entirely on your application. But if your projects have even a small chance of needing distortion data, the math changes fast.

And calibration — this one stung. I bought a used 2015 and skipped the calibration check, thinking, "what are the odds it's out of spec?" The odds caught up with me. The THD readings looked plausible; they were off by roughly 30%. It took a week of chasing a nonexistent distortion problem before I pulled the calibration history and saw the certificate had lapsed 14 months earlier. The 2015's basic DC accuracy is specified at 0.002% of reading — but only after a valid NIST-traceable calibration. So when you compare prices, compare calibrated prices. An uncalibrated meter is a paperweight with a good story.

Dimension 3: Usability, Menus, and Multimeter Training

Here's something you won't find in any datasheet: the 2015's THD functions add menu layers. The THD measurement lives as a secondary function behind the AC voltage key, and I spent — no exaggeration — forty minutes hunting for it the first time. The manual calls it "straightforward." The manual is written by engineers who've forgotten what it's like to be new.

That matters for multimeter training. A tech comfortable with handheld meters can get productive on a standard Keithley bench DMM in about twenty minutes. The 2015 is a different story. You have to understand what THD percent means versus dB, how the AC filter setting changes your reading, and why the fundamental frequency setting drives every distortion measurement. Without that context, the 2015 produces numbers that look precise and mean nothing to the operator.

I watched a technician confidently record a THD reading of 0.023% without realizing the fundamental frequency was set to 60 Hz while he was measuring a 1 kHz audio signal. The meter was fine. The training gap wasn't.

It's the same skill gap I've seen with other precision tools. I've answered my share of "how do I turn on this Mitutoyo micrometer?" questions from new techs — and watched the same people install a 4–20 mA transmitter on an oil flow meter without blinking. Give them a harmonic spectrum, and they're lost. The tool is never the whole story.

Conclusion: if you buy a 2015, budget for training, not just hardware. If the team only needs basic measurements, a standard DMM is the better fit — not because it's better, but because it's honest about what it demands from the user.

Dimension 4: Application Fit — Where Each Meter Earns Its Keep

Here are two real days from my bench.

Day one: I'm characterizing an audio preamp's output and need THD at 100 Hz, 1 kHz, and 10 kHz, plus the individual harmonic levels. The 2015 does the whole sweep without changing a single cable. I log the results over GPIB and move on. There's something genuinely satisfying about a measurement session that flows — the 2015 gives me that on audio days. This is where it earns every dollar.

Day two: I'm verifying the resistance of 500 current-sense resistors. Four-wire resistance, 100 readings per component, compare against tolerance. The 2015 behaves exactly like a standard DMM — because in this mode, it basically is a standard DMM. The THD front end is just along for the ride. I could have bought two used Keithley 2000s for the price of one 2015 and cut the QC time in half.

And the data logging side, which people forget: both scan and log the same way. If you're monitoring temperature, pressure transmitter outputs, or an oil flow meter pulse signal, the 2015 adds zero value over a standard Keithley bench DMM. The scanning, logging, remote control — identical.

Conclusion: the 2015 is a specialist generalist. It handles standard metering duty perfectly well, plus a narrow and deep set of THD functions. The more your work crosses into audio, power quality, or distortion analysis, the more the 2015 makes sense. The less it does, the more those dollars are dead weight.

Which One Should You Buy?

Straight answer, scenario by scenario:

Buy the Keithley 2015 THD multimeter if…

• You test audio equipment, amplifiers, or power supplies where distortion specs matter.
• You do power quality work, even occasionally.
• You want one box that handles standard measurements and THD, without a separate distortion analyzer eating bench space.
• You're stepping up to 6.5-digit accuracy and don't want to second-guess the choice later.

Buy a standard Keithley bench digital multimeter (like the 2000) if…

• Your work is DC-oriented: voltage, current, resistance, temperature.
• You already own a dedicated distortion analyzer or audio test system.
• You're equipping a lab where multiple techs will grab the meter for everyday readings — the simpler the menu, the fewer the "it just broke" reports.
• THD would be demonstration-ware: shown to visitors once, never used again.

One more note, from experience that started with a single-unit order.

When I was building my first test bench, I needed exactly one meter. One. I called a distributor and spent twenty minutes asking basic THD questions. The rep could have rushed me off the phone — it was a single item, after all. Instead, she walked me through the 2015's specs and told me where the used-market traps were. That one-meter order started a relationship that's since grown into tens of thousands of dollars in equipment purchases.

Small doesn't mean unimportant. It means potential. If a supplier treats your one-meter inquiry like a nuisance, find another supplier.

The meter isn't expensive. The wrong meter is.

That's the lesson four mistakes taught me. Compare these two honestly — not just the prices, but the work you do, the training your team has, and the projects you see coming. The right Keithley bench digital multimeter will still be on your bench a decade from now. The wrong one will just be a reminder.