A MAN with one clock knows what time it is, goes the old saw, a man with two is never sure. Imagine the confusion, then, experienced by a doctor with dozens. Julian Goldman is an anaesthetist at Massachusetts General Hospital in Boston. Like many modern health care facilities, it has become increasingly digitised and networked, with hundreds of high-tech medical devices feeding data to a centralised electronic medical record (EMR), which acts as both a permanent repository for health information and a system that can be accessed instantly by doctors to assist with clinical decisions.

After beginning to administer blood-thinning medication during an urgent neurological procedure in 2005, Mr Goldman noticed that the EMR had recorded him checking the level of clotting 22 minutes earlier. The correct interval was 30 minutes and he had, in fact, waited that long. His digital coagulation monitor was running eight minutes slow. Had Mr Goldman left the operating room during the procedure, another doctor might reasonably have assumed that the medication was acting swiftly and and reduced the patient's dosage. That might have led to a life-threatening blood clot.

Mr Goldman was concerned. If one critical device was set incorrectly, how many others were also wrong? He secured a grant for a comprehensive survey of four prestigious East Coast hospitals: Massachusetts General, and Brigham and Women's in Boston, the Hospital of University of Pennsylvania in Philadelphia, and Johns Hopkins in Baltimore. It was used to pore over kit ranging from medical monitors to heart-lung machines, infusion pumps delivering drugs and ventilators providing oxygen, as well as hundreds of wall clocks. Each device's clock was compared with a mobile phone synchronised to the US official time.

The results, presented recently at the CPSWeek conference in Beijing, are unnerving. Of over 1,700 devices checked, only 3% were found to be accurate to within three seconds. One in five were off by more than 30 minutes; one ultrasound machine was running 42 years (and some minutes) early. The average error was a staggering 24 minutes.

Such discrepancies might have been responsible for drug dosing errors, missed or repeated procedures and therapies that lasted longer or shorter than necessary. In 2007 Andreas Valentin, of the Rudolfstiftung Hospital in Vienna, examined 113 intensive care units in 27 countries, finding that mistimed medications were the leading error in the administration of intravenous drugs, accounting for nearly half of all mistakes.

It is impossible to say how many could be blamed on unsynchronised devices. The reason is that the information is hard to pin down. If the data in the EMR do not match the doctor's recollection, it is impossible to say which erred, man or machine. Not everyone will photograph the wayward clock, as Mr Goldman did with the clotting machine's.

Some records systems automatically reject data that look untimely. Since the EMR is updated constantly, data from devices whose clocks are way off would simply never be recorded. Others might bury current information in older files. Worse, they may insert the data into the EMR when the patient they concern has left the given clinical environment and another has come in. All this calls into question the veracity of the EMR and makes it difficult to reconstruct adverse events. It is a slew of malpractice suits waiting to happen.

Even devices that are in sync give hospitals headaches. Daylight saving time corrections twice a year require tedious manual tweaks that the MD PnP Program, an initiative supporting networking standards for medical devices, estimates cost American hospitals over $17m annually. At Massachusetts General, a patient-monitoring system deletes an hours' worth of data when rolling back from 2am to 1am every autumn, while drug pumps are kept permanently on standard time, so they are (at least) one hour off for half the year.

Meanwhile, a simple solution has been around for decades. Network Time Protocol (NTP) was developed in 1985 as a way to synchronise digital devices, and is what keeps computers and mobile phones co-ordinated to the last leap second. A hospital can easily host its own NTP server, connected to ultra-accurate atomic clocks in orbit via the Global Positioning System.

The rub is that few of today's assorted medical devices (or wall clocks for that matter) can tap an NTP server. Regulators like America's Food and Drug Administration have never insisted that medical-device manufacturers include this feature. Adding it now would mean rewriting software, retesting devices and resubmitting them for approval. This, too, carries considerable costs.

Still, they may be ones the industry will have to bear. In the United States, the Department of Health has proposed new "meaningful use" rules that would require EMR systems to include NTP technology starting from 2014. If you find yourself in need of a procedure before then, you might want to ask your surgeons to synchronise their watches and device clocks before they get cracking.