Consistent monitoring: read the trend, not the snapshot

The panel said closed

At about 4 a.m. on March 28, 1979, a failure kept the main feedwater pumps at Three Mile Island's Unit 2 from sending water to the steam generators, and the reactor shut itself down. Pressure rose, and a relief valve opened to bleed it off, as designed. Then the valve stuck open. "Instruments in the control room, however, indicated to the plant staff that the valve was closed," in the words of the Nuclear Regulatory Commission's account. Cooling water poured out as steam, and "as alarms rang and warning lights flashed, the operators did not realize that the plant was experiencing a loss-of-coolant accident."

The second failure was quieter, and for a patient it's the more useful one. The reactor had no instrument that showed directly whether water covered the core. So, the NRC says, the staff "assumed that as long instruments showed that the pressurizer water level was high enough, the core was properly covered with water too. That wasn't the case." They were reading a stand-in number and treating it as the real thing. The steps they took uncovered the core, and it partly melted.

Your yearly checkup can work like that pressurizer gauge. A blood pressure taken in an exam room records one moment, in one room, on one day. It tells you something true. It isn't the whole system, and it is very easy to read it as if it were.

Two principles, one habit

Weick and Sutcliffe list sensitivity to operations and reluctance to simplify as separate principles. The Agency for Healthcare Research and Quality's primer describes the first as keeping situation awareness, understanding how current conditions affect safety, and the second as looking for underlying causes while accepting that the work is complex. Dr. Scott folded both into a single step, because for one person they come to the same act: paying attention to what your body is doing now, and declining to explain it away.

Her original slide is plain about who holds that job.

"Only you are in a position to stay 'in tune' with your body. ... Health is more than just a blood pressure reading or a fasting lab result. It's how you feel on a daily basis." Dr. Scott, from the original SCOTT Protocol

There's a balance in that slide worth keeping. It calls knowing your numbers "critical for wellness," and it says your personal intuition "may serve as a harbinger that something is wrong, long before a diagnosis indicates the presence of disease." In the same breath it warns that hypochondria "on its own is not healthy or productive." Consistent monitoring is both halves: a log of numbers and a log of how you feel, each read for change rather than for alarm.

What counts as monitoring

Dr. Scott's original description of this step names two kinds of watching. One happens at home: "continually monitoring vitals such as weight, blood pressure, or blood sugar." The other happens at the clinic: "in-office diagnostics on a regular basis, such as blood panels, pap smears, PSA testing, mammograms, colonoscopies, and more." Neither replaces the other. A home cuff can't find a polyp, and a colonoscopy every ten years says nothing about this month's blood pressure.

Which office tests you need, and when, depends on your age, sex and history. The U.S. Preventive Services Task Force publishes the core list of recommended screenings for adults (as of October 2026), and the screening timeline turns it into a list for your age. The habit underneath every test is simpler. In Dr. Scott's words, the protocol asks you to "note variances in how your body is functioning and recognize the opportunity to investigate and not simplify a response."

Trends, not snapshots

The American Heart Association reaches for the same image this site does: "One blood pressure measurement is like a snapshot. It tells what your blood pressure is at that moment. A record of readings taken over time provides a more complete picture." The chart below shows what that means. It's an illustration with simulated readings, not a real patient: two years in the life of someone who feels fine the entire time.

One person, two ways of watching

Two years of a healthy-feeling adult's systolic blood pressure. Switch between what three yearly checkups show and what a weekly home reading shows. Illustration with simulated readings.

Three office visits Weekly home log

Three checkups, three reasonable-looking numbers, until the third one isn't.

Show the numbers

Period	Average home reading (mmHg)
Months 1–3	120
Months 4–6	120
Months 7–9	123
Months 10–12	126
Months 13–15	129
Months 16–18	136
Months 19–21	139
Months 22–24	140

Office visit	Reading (mmHg)
Month 1	123
Month 13	128
Month 24	147

Thresholds from the 2025 AHA/ACC high blood pressure guideline (stage 1 is 130–139 systolic; stage 2 is 140 or higher), summarized by the American College of Cardiology. Readings are simulated for illustration.

Switch to the weekly log and find where the line crosses 130. That is where stage 1 high blood pressure begins under the 2025 AHA/ACC guideline, and in this illustration the home log shows the crossing months before the next checkup can.

The normal reading that isn't

Sometimes the office number is simply wrong about the rest of your day. In masked hypertension, blood pressure reads normal at the clinic and runs high outside it. A 2017 analysis of U.S. data estimated that 12.3% of adults with normal clinic readings, no heart disease and no blood pressure medicine had masked hypertension: about 17.1 million people. The authors note that it is associated with a higher risk of organ damage, cardiovascular disease and death.

That's one reason the American Heart Association recommends home monitoring for everyone with high blood pressure, and notes that it can also be used to confirm a diagnosis. A home cuff is the instrument the control room was missing: a direct reading of the thing you care about, taken where you actually live.

What nobody has told you yet

A trend you never measure can't warn you, and most of the distance between having a condition and controlling it starts with not knowing. Among U.S. adults with high blood pressure, using the current 130/80 definition, 59.2% have been told so by a clinician, 51.2% are being treated, and 20.7% have it below 130/80, according to the National Center for Health Statistics (2021 to 2023 data).

Diabetes follows the same pattern. The CDC estimates that 11 million American adults have diabetes that hasn't been diagnosed, more than 1 in 4 adults with the disease, and that roughly 8 in 10 of the more than 115 million adults with prediabetes don't know they have it.

The overworked explanation

Reluctance to simplify is the harder half of this step, because a simple explanation is almost always available and almost always sounds reasonable. Dr. Scott's original description of the step includes an example worth memorizing.

"My headache, thirst and blurred vision are just due to working hard and lack of sleep. In actuality these are symptoms classic of diabetes." Dr. Scott, from the original SCOTT Protocol

The story fits a busy life perfectly. Busy people are tired, forget to drink water and squint at screens all day. But feeling very thirsty and blurred vision both appear on the NIDDK's list of diabetes symptoms, along with urinating often, feeling very hungry even after eating, fatigue, sores that don't heal and frequent infections. The American Diabetes Association's 2026 Standards of Care accept a random blood sugar of 200 mg/dL or more as enough for a diagnosis when it comes with classic symptoms. The overwork story costs nothing to tell yourself, which is exactly why it deserves suspicion.

Reluctance to simplify doesn't mean assuming the worst. It means holding off on the easy answer until something has actually ruled out the harder one: in this case, a blood test your clinician can order.

Don't fly on one gauge

The opposite failure is watching one number so closely you lose the rest. On December 28, 1978, United Airlines Flight 173 circled Portland, Oregon, for about an hour while its crew worked on a landing gear problem, then crashed in a suburb when its engines ran out of fuel. The National Transportation Safety Board found that the captain's inattention to the fuel state "resulted from preoccupation with a landing gear malfunction and preparations for a possible landing emergency."

Patients do this too, usually for good reasons. Picture someone treated for high cholesterol who watches that number faithfully for years and never takes a blood pressure reading at home, or someone working hard on their weight who stops noticing how little they sleep. Sensitivity to operations means keeping the whole panel in view, which is why the American Heart Association describes heart health as eight measures rather than one.

Know your numbers

Here are the current thresholds for the two numbers most adults should know, with room to type in your own. They describe readings and lab results, not people. Only a clinician can make a diagnosis, and your own target may differ from the general one. The third tab steps back to the American Heart Association's wider dashboard.

Before you trust the number

A home reading is only as good as the way you take it. The American Heart Association recommends an automatic, cuff-style monitor that goes on the upper arm, and says wrist and finger monitors give less reliable readings. Choose one that has been validated: a pharmacist can help, or you can look it up at validatebp.org. Make sure the cuff is the right size for your arm. Then take the monitor to your next appointment so your clinician can check that you're using it correctly and that it agrees with the office equipment, and plan to bring it in once a year.

After that, the reading itself is a short checklist, the kind pilots run before every flight instead of trusting memory.

One line from the AHA deserves a paragraph to itself: don't stop taking blood pressure medication because of your home readings without checking with your clinician first.

Running it week to week

Monitoring only works as a habit. In practice it can look like this:

• Same chair, same time of day. Both the AHA and the CDC say to measure at the same time each day. Ask your clinician how often; the CDC notes that people with high blood pressure may need to measure more often than people without it.
• Write every reading down, or use a monitor that stores them, and bring the record to every visit.
• Read the average, not the last number. Once a week, look back over the log. One high reading is not a crisis. A month of readings drifting upward is a conversation to have with your clinician.
• Keep a line for how you feel. New headaches, thirst, swelling, getting winded on the stairs: note them with dates beside the numbers. That is Dr. Scott's "how you feel on a daily basis," written down where a clinician can use it.

None of this takes more than a few minutes a day. Over a year it adds up to the thing a single checkup can never give you, which is the direction you're heading.

Last updated October 16, 2026. Guidance cited here was current on that date; clinical guidelines change, so check with your own clinician. See our editorial policy.