Heliochronometer

Installation instructions (Northern Hemisphere)

Introduction

1. The Heliochronometer which you have purchased is a precision instrument which will read accurate time provided that it is set up and aligned with sufficient accuracy. The purpose of these Instructions is to take you through that process step by step.

Identifying your model

2. There are two basic models of the Heliochronometer.

fig 1

Fig 1 above illustrates the Standard model which incorporates the facility to remove the unit indoors when not in use and then, simply and accurately to re-seat it on locating pins when next required in the garden. The Static model, which is for fixed installation at it's garden site, varies from the Standard one only in so far as it does not incorporate the Intermediate Plate. It also has just one, central, Locating Spigot whereas the Standard model has three.

What you will need

3. As basic tools for your initial installation, the wooden transit box includes a small compass, a spirit level, a small squat screwdriver, a 5mm Allen key as well as three brass screws and appropriate rawlplugs. There are also three small coins (para 12 explains!) In the case of the Static model, there will also be an additional set of Lateral Locking Screws. These will be theft resistant Allen bolts. In addition to this, you will need:-

A drill and 6mm masonry bit
A larger, more powerful, screwdriver
A 10mm open jaw (ordinary) spanner

4. You will also need to know your Latitude and Longitude. You can discover this from an Ordnance Survey Map or, failing that, the local Library ought to be able to help. You also need a rough awareness of the Magnetic Variation. Para 9 below gives assistance in this regard as far as the British Isles are concerned. GSD can give telephone advice as far as other locations are concerned.

Site and Plinth

5. Select a site in comparitively open ground and so positioned as to be subject to the rays of the sun for as much of each day as possible. On a firm and stable foundation, erect a pedestal made of stone or brick or other rigid substance and, ideally, about 39" high. The top must be as level as possible and large enough to accept the 9" outer diameter of the Levelling Plate which doubles as the base for the instrument. It is recommended that you use the spirit level in the final, cementing, stages, of this operation. GSD can recommend or supply a suitable plinth and, in such event, will provide specific installation instructions

Phase 1 - The Levelling Plate

6. This is one of the most critical operations of the whole installation. The Levelling Plate must be aligned, more or less North/ South but, more particularily, it must be absolutely level.

7. Carefully extract, firstly the false top and then the Heliochronometer from the transit box. Finally lift out the Levelling Plate which will have remained in it's recess in the bottom of the box. Place all accessory parts (foresight, backsight, screws, etc) in a safe place.

8. The Levelling Plate must now be placed on top of the centre of the pedestal and aligned so that the main axis of the instrument faces South (to within 10 degrees). To facilitate this evolution, some parallel lines are pencilled on the Levelling Plate with South annotated (S) at the relevant end. These marks can be erased after use but are, in any event, obscured by the rest of the installed instrument. One must now make use of the compass and of the magnetic Variation correction appropriate at the site.

9. The Variation for Great Britain lies in North/South bands across the country. It slowly increases from East to West. For the purposes of this exercise, it is sufficient to know that the North/South band through London is 4 West, that through Bristol is 5 West. Cornwall is 6 West and Belfast is 7 West. The Compass provided must now be adjusted to incorporate this Variation. Ignoring the position of the actual compass needle, rotate anti clockwise the ring on top of the compass circle until South comes around to the longer end of the rectangular baseplate. Continue a little further anti clockwise until the Westerly Variation is reflected to the right of South. It can also be measured against the white fixed head marker under the ring. If it had been Easterly, the variation would have been to the left. Fig 2A shows the compass set up for Variation 8 West.

fig 2a

10. Place the Levelling Plate centrally on top of the plinth. At this point, the operation is hindered by the fact that, although the heliochronometer is basically all brass and the locating spigots are stainless steel, many of the plinths in current use have a steel reinforcing rod running up their centre. Thus it is not possible to position the compass on top of the Levelling Plate and simply rotate the combination until the correct alignment is achieved.

11. Instead, one must initially rotate the Levelling Plate until the pencilled aligning lines are very approximately North/ South. Then stand about 3 feet to the North of the Plinth and, holding the compass at about chest height, rotate it until the north seeking (red) needle is aligned with the parallel lines within the compass circle. They are now running magnetic North/South. The parallel lines on the rectangular base of the compass are now deflected to the right (by the Variation) and are running true North South.

With trial and error and by sighting through the transparent compass, one now adjusts the alignment of the Levelling Plate until the pencilled lines are running parallel (or nearly) to those in the rectangular part of the compass in your hand. Fig 2B attempts to illustrate this process.

fig 2b

The Levelling Plate is now pointing true South within a few degrees. Such temporary inaccuracy is well within the scope of subsequent adjustment mechanisms in the heliochronometer.

12. Using a pencil through the three countersunk screw holes, Fig 3, mark the surface of the pedestal with the positions for the three screws.

fig 3

Remove the Levelling Plate, being sure that the required screw holes are clearly identified. With a drill and 6mm masonry bit, drill to a depth of 36mm and insert the three rawlplugs provided. Replace the Base Plate and lightly secure it with the three 1 1/2" size 8 brass screws provided. Whilst the screws are still about 10mm proud of their countersunk holes, lift the edges of the Levelling Plate and insert a small flat coin under each of the Levelling Screwbolts. Fig 3.

This is to stop these bolts slowly grinding themselves into the top surface of your plinth. (French 5 centimes pieces are ideal and three are provided). Continue screwing in the brass screws until they just go beneath the surface of the Levelling Plate. The countersunk holes are further recessed in order to allow an additional further 4mm of screw movement which gives extra s flexibility of movement necessary in the levelling process that immediately follows. It is here that accurate use of the Spirit Level is critical. Place it as close as possible to the central spigot. It is advisable to consider this important issue in two axis. Those of North/South and East/West and to deal with each of these in turn. It is a progressive process, correcting East and/or West and then South. Repeating as necessary. Do not correct at the North.

If the bubble does not settle in the centre of the levelling circle, it indicates that the pedestal top is not completely level - and the situation must be rectified by slightly tilting the Base Plate. Note that the bubble will always go towards the highest point. Thus, if the bubble has settled to your left, it means that you must raise the right side of the Base Plate and vice versa. It is advisable to consider the issue in just two axis - those of North/ South and of East/ West. And deal with one axis at a time, correcting East and/or West and then South. Do not correct at the North end.

If any of the three correcting ends of of the axis needs to be raised/lowered, slacken off the locking nut on the relevant Levelling Screwbolt and turn the screw (clockwise to raise) until the bubble has re-centred.

13. When finally satisfied with the level of the Levelling Plate, screw the brass screws virtually the whole way down but only finger tight at this stage. Check that the Levelling Plate remains level in both planes. Holding the Heliochronometer so that the Vernier Scale (Fig 1) is to the West, place it carefully onto the Levelling Plate. You will need to rotate the Standard model as necessary to seat it on it's Locating Spigots. Check that the Latitude Dial (Fig 1) is set to exactly 90 degrees and now use the spirit level to check that the Dial Plate is also exactly level. Again, both East West and North South.

A tiny amount of extra adjustment might be necessary but this must be implemented as, in the final analysis, the most important datum is that, at 90 degrees of Latitude, the Dial Plate should rotate on an absolutely level platform. If any such extra adjustment is necessary, remove the Heliochronometer, slacken off the three brass screws - but not so that they obtrude above the top of the Levelling Plate and replace the Heliochronometer.

Make any final adjustments of the Levelling Screwbolts and, constantly checking that the Dial Plate remains level, tighten the locking nuts on the levelling screws. For this, you need your 10mm ordinary spanner.. Then remove the Heliochronometer again and, finally, fully tighten (into the top of the plinth) the securing screws.

Aligning the Spine

14. Replace the Heliochronometer on the Levelling Plate. In the case of the Standard model further rotation of the device cannot occur until the Lateral Locking Screwbolts (Fig 1) are removed. Do this, again keeping them in a safe place. The Lateral Locking Screwbolts of the Static model have not yet been fitted. Both models therefore, are now free to rotate.

The Spine, Fig 1, of the instrument must now be aligned with South. Rotate the Heliochronometer until the Vernier Scale is to the West. Again take up position three feet to the North and bring the compass to chest height. Visually sight down to the Heliochronometer. On this occasion, rotate, with your free hand, the Base Plate and, indeed, the whole instrument until, as near as possible, the Spine is aligned with the lines on the flat rectangular part of the compass. The Spine is then, near enough (at this stage), pointing due South.

15. Using the Lateral Locking Screwbolts, secure the Base Plate, finger tight, in this position. For the Standard model, replace the screwbolts recently taken out. For the Static model, there is a choice. Either use the brass screwbolts or the steel Hex (theft discouraging) screwbolts - for which the Allen key is provided.

16. In the interests of clarity, Fig 1 shows, on the Intermediate Plate, only one screw hole to marry with the Lateral Locking Screwbolts coming down from the Base Plate. In fact there are, on both the Intermediate Plate (Standard model) and the Levelling Plate (Static model) a range of screwholes in order to be sure that there is at least one suitably placed for the Locking Screwbolts.

Latitude

17. At the hub of the Latitude Dial is a large brass screwbolt. Using a screwdriver, loosen this and rotate the Dial until the correct Latitude, to the nearest half degree, is reflected at the bottom. (Fig 1). Tighten up the hub screw bolt, using the strongest screwdriver available. This should not need to be adjusted again and needs to be tight enough to resist any undue pressures or disturbance.

Longitude

18. Setting the Longitude is accomplished by moving the middle plate of the Vernier Scale. This is released by unscrewing the Longitude Locking screw to be found, Fig 4, on the underside of the Vernier Scale.

fig 4

The adjustment depends how far your site is East or West of the nearest Prime Meridian. In this context, Prime Meridians are those which occur every 15 degrees around the globe starting at the Greenwich meridian of 0 degrees. Moving East, Standard Times advance by one hour at each, 15 degree, Prime Meridian. Usually, countries adopt as their Standard Time that which relates to the Prime Meridian which passes through their territory. Geographically wide countries will need more than one Standard Time.

19. The resultant calculation and adjustment in the United Kingdom is easy. Plymouth, for instance is 4 degrees West of the Greenwich meridian of 0, Canterbury is 1 degree East. Observers in these positions should simply slide the middle plate of the Vernier (note, at this stage the top plate will move with it) until the vertical datum line on the edge of the middle plate rests over 4 degrees West or 1 degree East respectively.

20. For observers further afield, the problem is a little more complicated. The Longitude of Miami, Florida, is, for instance, 80 degrees West. The nearest prime Meridian is 75 West - from which Miami is displaced a further 5 degreees West. Thus here the setting is 5 West. Equally, Rome, at 12 East is 3 degrees West of it's Prime Meridian of 15 East. At 20 East, Belgrade is 5 degrees East of the same Prime meridian. Etc, etc.

Correcting for Local Standard Time

21. Some countries adopt a different Standard Time from that dictated by their adjacent Prime Meridian. Additionally the majority of countries choose to alter their Standard Times mid year in order to achieve additional Daylight Saving during the Summer. The UK is no exception. British Summer Time is one hour in advance of the Standard Time derived from the Prime Meridian. The top scale on the Vernier allows us to correct for deviations from Standard Time - be they permanent or temporary, such as in British Summer Time. To correct for this, loosen the Standard Time Locking screw (Fig 4) and slide the top plate of the Vernier Scale.

22. In the case of Summer Time (in the UK and elsewhere), move the top plate to the right until the graduation marked -1 is aligned with the vertical datum line on the edge of the middle plate. As a point of interest, some countries (France is an example) use 'summer' time as their standard and go to double summer time in the summer. For them, the Standard Time Locking screw must be unscrewed, the top Vernier Scale removed, turned upside down and replaced. It will be seen that the Scale now allows the incorporation of double summer time.

Fine Tuning

23. Using the screws already supplied in the Sighting Crossbar (Fig 1), carefully screw on the Foresight and Backsight. The former (the short one) is inboard of 18 o'clock whilst the longer Backsight is inboard of 6 o'clock. The Heliochronometer is, at last available for operation. It only remains to fine tune the North/South alignment so that the raised end of the spine points precisely due South. In the absence of a gyro compass or a properly surveyed alignment for the location, it is acceptable to carry out the process backwords using a recently set and accurate timepiece. Or the time recorded, for instance, on Ceefax. Rotate the Dial Plate (Fig 1) until the relevant hour graduation on the main dial face is against the correct minute of time on the Vernier Scale.

The shadow of the Foresight should now fall, at least in part, on the Backsight. It is actually sensible to set it to read a few minutes after actual time in order to give yourself some 'fiddling time'. Further loosen the finger tight Lateral Locking Screwbolts and then rotate the Spine (and, indeed, the whole Heliochronometer) until, at the critical moment, the dot of sunlight shining through the aperture in the foresight impinges on the correct month as engraved on the figure of eight on the back sight. Update so that the dial reading (hours and minutes) is exactly the same as that indicated by your reliable timepiece and then tighten the Lateral Locking Screwbolts. They should need no further adjustment.

Operation

24. The Helichronometer, henceforth, should reflect the correct time whenever the Dial Plate is rotated until the dot of light shines on the relevant part of the figure of eight on the Backsight. This is an easy operation best achieved if one stands with one's back to the sun and slightly to one side of the instrument (so that one doesn't block the sun). Rotate the dial plate until the foresight points is sufficiently aligned so that it's shadow falls on the backsight. It will then be observed that this shadow is punctured by the small dot of light.

Refine your rotation of the dial plate until the dot of light straddles the line on the figure of eight where it is identified as relating to the correct month. The instrument is now precisely aligned with the sun and the fully corrected time will be reflected by the relevant hour graduation (on the Dial Plate) identifying the correct minute on the Vernier Scale.

Maintenance

25. If left unattended, the brass will tarnish and develop a verdigris sort of patina which some find attractive. If, on the other hand, you wish to keep it, or parts of it, polished and shiny, occasional application of ordinary brass metal polish is required. However, it should be remembered that too much polishing will eventually blur the edges and vernier scales.

In order to ensure a sharp reflection of the 'dot of light', the Backsight has a different patina. It has been specially glass bead blasted. Should this get tarnished, it will not interfere with the reading of the instrument. However, if you wish to buff it up, a small piece of softback sanding sponge is provided. Dipped in water and gently rubbed on the backsight will have the effect of cleaning the latter.

26 As already mentioned (para 2), the Standard variant is so designed that it can be taken off it's plinth and removed indoors at will. No re-setting or re-tuning is required. This has attractions from a cleaning point of view in addition to that of theft reduction.

The Static model can, of course, also be brought indoors, say for winter, by the expedient of unscrewing the Lateral Locking Screwbolts or their Allen key, theft reducing, substitutes. Before doing this, the scribing with a suitable sharp instrument of a small, unobtrusive vertical line joining Base and Levelling Plates will much reduce the amount fine tuning required when re-setting this variant of the instrument. One should then only have to repeat the procedure outlined in para 23.