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The Olympic Marathon Measurement - Mike Sandford's Narrative Account

I set out for London with my son Geoffrey around Midnight. We had a traffic diversion and did not reach what I thought was the agreed meeting point - The bottom of the Duke of York Steps until about 01.45. There was no sign of Hugh and David. Eventually I saw lights about 300m away towards Buckingham Palace. It was Hugh and Dave with the London Marathon support van. They had completed the layout and measurement of the calibration course and were waiting for the police escort and an official photographer.

David presented me with a measurer's high visibility vest of excellent quality with lots of useful pockets, IAAF/AIMS logos, and my name and "International Course Measurer" neatly printed at the breast pocket. There were no London Olympics logos, but then we all know about the very close control kept over the use of the official Olympics logos. Nevertheless it is something I now very proudly wear when measuring. David also brought one for Hugh. Another generous present from David was a couple of packets of Mag Nails, arguably superior to the PK nails I normally use in measuring. Thank you David.

Before long police on motor bikes started to arrive, eventually about 8 in all. Finally the photographer from the Wall Street Journal turned up. While these were assembling, David and Hugh led me off to chalk a riding line 1.3 m from the cobbled strip around the Queen Victoria Memorial. They also marked a point we would aim for on leaving the Memorial where we would turn on to the right half of The Mall.

David's counter fails

At about 02:07, as we prepared for our first calibration ride, David announced his J-R counter was not turning. The tag was bent not engaging the spokes and also the large metal spur gear was seized. I removed his counter. It still would not turn. The slot for the gear spur gear had been some how clamped tightly on the spur gear. I tried to lever it apart with a screw driver to free the gear, without success. David's front wheel had a quick release mechanism which I always find slightly tricky. I suspected he may have had a 9mm hole counter and I thought it possible that tightening up the axle bolt he had clamped everything up too tight.

This was a considerable set back, since David being the official measurer had to have a working measuring bike. My first thought was to sacrifice my ride and offer David my bike. But then I realised he would be unfamiliar with the operation of my electrically assisted bike. So I removed the J-R counter with a 10mm axle hole from my bike and installed it on David's axle. It turned fine but the tag was too far from the spokes. I asked for some wire and Hugh went to look in his bag. Very fortunately Hugh discovered a spare old-style Jones-Oerth counter which he must have forgotten he had in the bag. So we installed this J-O counter. It needed its tags bending to engage the spokes by more than we could easily do by hand. My son Geoffrey who was accompanying me (not riding) came up with a pair of pliers on his all purpose pocket knife tool which did the job, and David then had a properly working counter. With considerable relief I put my J-R counter back on my bike. I would after all be able to measure.

Davids J_O Counter David's Bike with Hugh's spare J-O Counter installed

It was not all clear to me how the gear had become clamped. I can only conjecture that when installing it on the quick release axle the counter's axle hole had been slightly misplaced so that tightening axle squashed the bearing plates onto the gear. At measurement seminars I have occasionally experienced problems when fitting a J-R counter to some bikes if wrongly placed on a quick release axle. It is certainly possible to have some resistance to turning if not optimally placed, but I have never had any counter clamp up solid to such an extent that it would need tools to free it.

Pre-Measurement Calibration

At 02:19 we were ready again for the calibration which then proceeded very smoothly. During their taping before I arrived, Dave and Hugh had stuck pieces of tape to the road at the end of each tape length and marked the exact position with a pen. My first reaction was one of a bit of concern that the course ends had not been nailed. What would happen if the tape became dislodged before we had completed our post measurement calibration. It was later pointed out to me that the end points were exactly in line with the East faces of the base of two lamp posts at the kerb about 30 cm to the side, so it would be possible to relocate the ends sufficiently well had the tape been disturbed. I imagine there might have been some caution about not having permission to bang nails into the pristine red tarmac of The Mall.

Small Lap measurement

We set off round the course at about 02.30, the police riding ahead and behind, blocking side roads and closing down the lane ahead when the SPR took us onto the wrong side of the road. The process they use is one of repeated leap frogging. Once our procession of 3 bicycles had passed, the police motor bike guarding the side road weaved past us and took up position on the next unguarded side road ahead. I imagined that this must be what it is like to be in a Royal or VIP procession around Central London. Although as the police motorbikes expertly weaved past we cyclists it made me think also of the TV images of the Tour de France.

We had numerous brief stops to record our readings at intermediate distances, and for the police to clear traffic problems ahead. Central London is surprisingly busy between 2 and 4 am. Hugh, of course knew exactly where we needed to stop. All I had to do was keep close behind Dave, noting exactly where he and Hugh had stopped to take the reading. Sometimes the reference point was away to the side, so I may not have exactly judged the right point to take the reading. I tried to note exactly where David stopped to take his reading rather than judge alignment with some more distant landmark.

At first Hugh appeared to be rushing off too quick for David who said that he felt that he was being hurried too much. But after a few miles we all settled down. I really enjoyed the ride - both the precsion of the bike riding and glimpses of London streets which I did not know.

David's plan had been to do an intermediate calibration after completing the small lap, but when we reached the finish line after lap one we went straight ahead with measuring the large lap. I don't know if this was due to concern over the time which we had lost at the start, or whether it was just forgotten. In the event missing this intermediate calibration check did not make any impact on our calibration since there was very little temperature change during the measurement, and for all 3 riders the pre-measurement calibrations were very close to the post-measurement calibrations.

Large lap measurement

On our second lap down the 4 lane Northumberland Avenue, we were on the right facing a huge lorry stopped ahead of us. The police expertly shuffled the traffic around so the lorry could cross to its right in order to leave the shortest line clear for us to ride.

As we went west there was another hold up for several minutes due to road maintenance activities which closed the Victoria Embankment where it dipped under one of the bridges over the Thames (Blackfriars bridge I think.) I chatted to a police lady on her motor bike. The Wall Street Journal photographer jumped out of the London Marathon support van and photographed us from every angle. He was strangely attracted by the glowing digits of the voltmeter measuring the state of the battery on my electrically assisted bike. I did explain that it was nothing to do with the measuring process, nevertheless this photo made it into a slide show on the WSJ web site to illustrate the article by Joshua Robinson which appeared in the WSJ on 20 June.

Once the road was clear we headed off under Blackfriars Bridge. Here I can be seen tracking David. Hugh is hidden in front.

I had my electric bike mostly on medium assist the so I could easily cope with the slight incline up from the Embankment. Going though Paternoster Square after St Paul's Cathedral, Hugh missed his intended reference point for 20 km so he improvised another about 70 m further on.

At the North side of Paternoster Sq. there was a temporary works barricade in place. Hugh and David performed the classic measurer's maneuver - with front wheel touching the barrier, note where the back of the bike is. Clamp front wheel list back to the noted point and wheel forward to the barrier again. Clamp wheel and carry around the barrier to start measuring again with the back of bike touching the barrier. Seeing where they ended up riding on the other side, I judged I could just lift my bike sideways a couple of metres and ride a reasonably satisfactory line to the next bend.

When we reached the refence location for the Eastern turn round on Tower Hill, I noted that Hugh's description said end of central divide at Roman Wall. I thought that is interesting, I did not know that London still had Roman walls, and I wondered where the wall was. Only much later via the web I found out that it is still standing high on the North side of Tower Hill complete with a statue of the Emporer Trajan which I will have to go and view one day. I learnt some history as a result of the measurement ride!

The other occasion when we differed somewhat in line taken, was when dealing with 3 or 4 parked cars as we returned along the long bend of the Embankment travelling towards Big Ben. Hugh veered out gently over 50m + to pass around some of the vehicles. Whereas David stayed at the kerb and offset out and back immediately around each vehicle. I followed David of the first of these vehicle obstructions. But for the subsequent ones I judged that, since the the road was so nearly straight, Hugh's veer out and back was good enough and did not risk any small errors in judging the 90 degree of the offset if I had tried to use that method.

We reached Big Ben at 04:23, and arrived at the finish line soon after without further incident. So it took about 2 hours for a total of 10.2 miles to be measured so you can see we had spent quite a bit of the time stationary, waiting for the route ahead to be cleared, in discussion, or writing down our splits.

Post Measurement Calibration

The police bikes were dismissed and we calibrated again without incident. The sticky tape was still in place. The temperature had dropped by 1.1C to 10C, and my calibration had barely changed. I was happy I had a good set of data. Likewise with David and Hugh who set about calculating their distances, while Geoffrey and I set up to use my laser to check the calibration course length.

Laser check of cal course

Here is how I transport to calibration courses my laser rangefinder with its ancillary equipment: a retro reflector and an equatorial telescope mount used for precise pointing over ranges up to the maximum of 250m

laser rangefinder

Below you see me on The Mall with laser in position about to pedal down to the Buckingham Palace end of the calibration course. The measurement is taken with the bike's kickstand deployed, so that the bike acts as stable tripod - overall an arrangement much better than the flimsy tripod and cheap alt-az pointing mount which came with the Bosch Laser Rangefinder


As you can see in the above photo the rising sun had just started to illuminate Buckingham Palace. A few minutes later when I was at the west end of the calibration course ready to take my first reading the rising sun was shining straight into the viewfinder of the laser, and I could not see my retro reflector to line up the laser spot. That was a new problem for me, but then I have not previously used this equipment firing towards the rising or setting sun. I decided to switch directions, moved the retro reflector to the west end and set up the laser on the bike about at about the midpoint of the calibration course 160 m to the east. I now had no trouble seeing the retro reflector in in the viewfinder and guiding the laser spot on to it using the slow motion knobs on the equatorial mount. Once on target, the retro-reflector can be seen with the naked eye to light up red even with the rising sun shining fully on the target.

I was very careful not to send the laser beam into the windows of Buckingham Palace behind, I did not want to get arrested by the Guards. I find the safe way to avoid such an accident with other road users or indeed residents is to make sure the laser beam in pointing towards the road before it is switched on, then carefully adjust the laser pointing controls so that the beam approaches the retro reflector from the road direction rather than the sky direction. The laser is Class 2, so eye safe provided you do not stare into the beam.

The first sign of confusion over the calibration course length started at this point. When we did the pre-measurement calibration I had been told one distance but later, while I did my laser measurement, David and Hugh recalculated and reported a revised value of 328.56 m (I did a quick on the spot calculation of of my laser readings but there were still some more corrections to apply and which I completed when I got it on a spreadsheet at home the laser gave 328.621 m. This was the start of a long saga during which the cal course length calculations were gradually refined and which I will describe in section on data analysis.

Hugh and David agreed very closely on their measurements ride distances. I put off doing my calculations until I had everything on a spreadsheet at home.

Geoffrey and I headed by car to David's hotel to collect some J-R Counters. Hugh and David cycled. We had a long wait at the hotel before they arrived. David had fallen off riding over a speed control bump (or sleeping policeman as they are commonly known). He had hurt his knee, but was still just about mobile. Not a good end to an otherwise memorable and successful night's work. We collected the counters and set off for home, stopping en route for coffee in order to keep awake.

Here is a summary of the data analysis which took place over the next three weeks or read my detailed account.

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