We were at the 12th-century St Peter's Church in Hanwell near Banbury in Oxfordshire. According to Edward Martin, my companion for the day, its walls have just about the finest collection of medieval scratch dials, or mass dials, to be seen on the outside of any country church in the land.
For Mr Martin, these odd arrangements of medieval graffiti have a magnetic appeal. He has been a mass dial addict for 16 years - ever since he was musing on mortality outside the church in which his son was to be married and spotted some odd scratchings on the ancient stones.
It was the first of some 800 of these primitive time-telling devices that he has subsequently pored over and meticulously recorded.
Today Mr Martin heads a team of 10 volunteers, all members of the British Sundial Society, who spend their leisure hours peering at mass dials, most of which are almost invisible to the untrained eye.
In all but a tiny handful of cases the gnomon - the metal rod that casts the sun's shadow - has disappeared, making it doubly hard to spot the tiny scratches that mark the site of these early timepieces.
As the name suggests, the dials were used to tell the times of mass. But that is just about all that the experts agree on. Mr Martin and his team are forming a variety of theories as to the other uses of the dials - mainly because they are so varied in style and because there are still so many they have not fully recorded.
"The accepted wisdom has been that there are about 2,000 mass dials scratched on the walls of old churches around the country. My estimate is that there are nearer 5,000. We have recorded well over 2,000 and have hardly touched some counties," Mr Martin said.
As I peered at what appeared to be a blank, flaking section of stone wall, trying to spot a mere handful of the 12 mass dials I had been told were on the south wall of the chancel of the church, I heard a loud "whoopee" from the nearby south porch.
Inside, an excited Mr Martin had rediscovered the faintest outline of a multi-ringed dial - a type that he regarded as more of a means of checking the calendar than telling the time of mass. "It's a beauty," he said.
But inside a church porch, where the sun never shines?
"Sometimes the porch was built after the mass dial was scratched into the wall," said a beaming Mr Martin. Easy.
"Studying mass dials can be a bit New-Agey at times," he conceeds. "Some of the scratchings you find, like many of the grotesque carvings found on early churches, smack of the days when many Christians had not quite forsaken their beliefs in the earth goddess and other pagan elements.
"Yet I am sure that many of the more sophisticated of these dials were really quite elaborate devices. I believe some of the calendar dials were put on churches simply because they were the only buildings that had dressed stone good enough to carve on. I also think that some of them are so precisely calculated that the sun would catch certain precise markings on the surface of the dial only on a particular day of the year, such as saints' days."
And if that day should be a dull one? "Ah, then the dial will not work," he said. "That is one reason why clockwork gradually superseded sundials as a means of telling the time in the mid-15th century.
"If you go searching for mass dials do not confuse them with bench marks, used to denote height above sea level. These can look like early mass dials but are generally very low down and cut much deeper. Don't expect to find mass dials on town churches - pollution, the elements and alterations to the buildings did away with most of them many years ago."
Edward Martin can be contacted at West Lodge, Thicknall Lane, Clent, Worcestershire DY9 OHJ. The British Sundial Society is at Barncroft, Grizebeck, Kirkby-in-Furness, Cumbria LA17 7XJReuse content