January 30, 2026
Description
This design was inspired by the Aten Heliochronometer Sundial, model B4003, designed and built in the 1990’s by the craftsman J.D. Gard of Tucson, Arizona. It’s a beautiful instrument made out of brass and aluminum, and it claimed an accuracy to within 1 minute. Unfortunately, only a few were built, and they are a relatively rare find today. The instrument was adjustable for latitude and longitude and corrected for the equation of time; i.e. Analemma, for accurate time telling in any time zone. It originally measured about 26cm high and 30 cm across, but this model is slightly scaled down to facilitate printing.
This design can be used in either north or southern hemispheres.
Figure 1: The Aten Heliochronometer Sundial, model B4003
For useful background information on heliochronometers; i.e. history, theory of operation, design, how to align and use, etc. refer to this useful printable: Heliochronometer - World's Most Accurate Sundial by yba2cuo3 | Download free STL model | Printables.com
Accurate to within 1 minute throughout the entire solar year from any location in the northern hemisphere. In practical terms, however, the accuracy will be determined by the quality of its construction, assembly, and precision of its final alignment;
UPDATE (12-26-24): Now supports the southern hemisphere! Make sure to grab the southern hemisphere main dial plate & analemma plate from the file section.
5-minute reading resolution on the main dial plate;
0 to 5 minutes reading resolution on a large, easy-to-read, secondary Vernier scale, in increments of 30 seconds;
The main dial plate was reduced to a ring, similar to those found on equatorial sundials, with the purpose of reducing material & print time without sacrificing accuracy or sturdiness;
1 degree latitude adjustment resolution;
Improved construction, using a minimum number of parts and a simplified but reinforced latitude adjustment protractor arm;
Replaceable Nodus cone with a small circular sight for improved reading resolution, or adopt your own custom design!;
Displays Local Mean solar time directly by computing corrections to the true, or apparent solar time. It achieves this by utilizing a visual-mechanical computer, also known as an analemma plate;
Converts Local Mean Time to Standard Local Time via meridian dial offset adjustments;
Please note that this version of sundial cannot be adjusted to display daylight savings time directly from the dial & therefore needs to be computed manually. This feature may be added in a future revision, depending on interest;
4 base options are available; 3 with integrated magnetic compass and levels, and 1 without. For compass/level options, refer to these printable links:
Assembly measures 180x200x200mm (W x L x H).
UPDATE (10-14-24): Added deeper cut mark versions for text, dial tick marks, etc. Look for the files with (deeper) in the name.
This heliochronometer was constructed out of ABS plastic filament. Check the Technical Details section & How was the Analemma Curve Designed into this Heliochronometer from this other printable: Heliochronometer - World's Most Accurate Sundial by yba2cuo3 | Download free STL model | Printables.com The analemma curve was calculated & plotted using MS Excel and then scaled to match the size (diameter) of this heliochronometer.
Curved vs. Flat Analemma Plates:
This model includes a flat plate analemma & fixed nodus. You may gain a bit more performance & reading accuracy from your heliochronometer if you adopt a curved plate design with a tilt adjustable nodus. If you prefer to swap these out, check out my other Printable designs at:
Printer brand: Prusa
Model: i3 MK2S
Supports: Yes
Resolution: 0.15mm OPTIMAL
Infill: 20%
Brim: Yes - 10 to 20mm
Filament brand: Doesn't matter
Filament material: ABS
Filament color: Doesn't matter
Special Notes:
Print in an enclosure for best results.
Use a darker color filament at a specific layer height to highlight the text if you have a single extruder.
Slow printer speed to 75% on top layers will improve tick mark production.
The construction of this sundial is relatively simple, making use of M3 & M4 hardware. A list of assembly material is provided below, along with where it's used. Also check the description associated with each file for more assembly details. All parts can be easily disassembled and reassembled to facilitate transportation.
If you live in the southern hemisphere, make sure to use the southern hemisphere analemma design in addition to the southern hemisphere dial plate.
All HW is Stainless Steel Button Head Hex Socket Head Cap Screws and Nuts, unless specified otherwise.
Qty | Description | Where Used |
|---|---|---|
4 | M4x15mm screw | Dial holder to dial ring; (fixes dial holder to dial ring) |
1 | M3x10mm screw | Pivot screw for Vernier Scale; (attaches to Alidade) |
1 | M3 square nut | For above |
1 | M3 Washer | For above |
3 | M4x16mm screw | Pedestal to protractor |
3 | M4 nuts | Used with above |
3 | M4x30mm screw | For base leveling. Screws in at ends of base |
6 | M4 nuts | Locks base levelling screws (top and bottom) once level. |
1 | M4x20mm screw | For Alidade (horizontal arm) pivot |
1 | M4 Nyloc nut | For above (Alidade pivot) |
1 | M4 flat washer | For above (Alidade pivot) |
2 | M4x20mm screw | Top screws for securing dial ring to protractor |
1 | M3x35mm screw | Bottom screw for securing dial ring to protractor |
4 | M4x20mm screw | (2x) attaches Pedestal to base. (2x) attaches Nodus and Analemma vertical arms to Alidade (horizontal arm). |
Deburring tool for removing excess plastic from printed parts
Hand Drill or Drill Press
2.5mm or 7/64" drill bit for enlarging holes for M3 tap
3.3mm or 1/8" drill bit for enlarging holes for M4 tap
M4 tap for making threads
Magnetic Compass
Circular Bubble Level
Alternatives: Smart phone with: 1) Compass or GPS app, 2) level app.
Can't stress enough the importance of having a well-aligned heliochronometer in order to make accurate and consistent readings.
UPDATE (01-02-25): As requested, please follow the new set of detailed setup instructions provided in the file section titled: How_to_Setup_your_Gard_Heliochronometer_Sundial-Detailed-Instructions-v1
Make sure your sundial has been aligned first!
If you haven't done so already, you must first adjust the dial plate for the difference in longitude between your location and your standard time zone meridian. See the example below on how to calculate the offset for Local Mean Time (LMT) to Standard Time (ST). With the alidade prime meridian mark (where the M3 screw is) aligned with the 0 mark on the Vernier secondary dial, rotate the alidade so that the 0 mark on the Vernier is aligned with 12 noon, then tighten the pivot screw so that the alidade is not able to rotate.
Unloosen the M3 screw securing the Vernier to the alidade and turn it slightly so that the 0 mark on the Vernier is at the time correction you calculated; i.e. difference between your standard time meridian and your longitude. Make sure not to move the alidade when rotating the Vernier scale. Once everything is set up, retighten the Vernier screw and unloosen the pivot nut so that the alidade is able to pivot again. Since this always remains the same, the Vernier will remain locked in this position once this step is done. The alidade 0 mark on the Vernier will now point at the indicated standard time.
To obtain the local mean time at any hour of any day, just turn the alidade until the sunlight passing through the sighting hole is centered on that portion of the analemma curve corresponding to the current month of the year. In this position, the pointer on the alidade will indicate local mean time.
Here is an example of how to read time with the secondary Vernier scale:
The sun spot cast by the Nodus sight is aligned onto the Analemma curve for the current month. In this case, it is September. It also happens to be the 25th, so the sun spot is just above the Autumnal Equinox indicated by the diamond shape; (see below)
The secondary Vernier scale located on the analemma side of the alidade is from 0 to 5 mins, in increments of 30 secs; (see below)
Therefore, for this example, the time is read as follows;
The zero mark on the Vernier indicates 10 mins past 3 o’clock on the dial plate; i.e. 2x 5 mins minor tick marks past the main 3-hour mark;
Now look for the next aligned marks on the Vernier scale that meet up with those on the dial plate. This happens to be at 3mins (± 30secs). Therefore, the time would read 3: 10+3mins = 3:13 PM PST.
Before learning how a heliochronometer really works, we need to understand the different types of times: i.e.
• A sundial shows True or Apparent Solar Time. Because the Earth's rotation is not constant, solar days vary slightly in length as it follows the ecliptic. This means that the speed of true solar time is not constant. It must be remembered that a sundial measures the hour angle of the true Sun as observed in the sky. In reality, the Sun’s true hour angle is due to two motions: diurnal motion, i.e. the motion of the Earth as it turns on its axis; and annual motion, i.e. the apparent eastward displacement of the Sun along the ecliptic. More about this later;
• Mean Solar Time is based on the length of a mean or average solar day, which is 24 hours long. It moves at a constant speed along the celestial equator. All hours have the same length regardless of the season. Mean solar time might be faster or slower than the true solar time, depending on the time of year;
• Local Mean Time (LMT) is the Mean Solar Time for a specific location on Earth. It is the same for all locations that share the same longitude;
• Standard Time (ST) is also referred to as the official time of a region, ascertained by the distance from the Prime Meridian of the meridian running through the area. For example; Pacific Standard Time (PST) → (UTC−08:00), has a prime meridian at 120 degrees longitude. LMT can easily be derived from ST by adding or subtracting 4 minutes for each degree away from the prime meridian, or 360°/24h = 15° for every time zone hour. It follows the simple relationship of 1 hour or 60 minutes for every 15° of longitude; or 4m per degree.
Converting time & setting your dial plate to convert to ST :
The relationship between your sundial time & your actual clock time is as follows:
True Solar Time + EOT → Local Mean Time + Longitudinal Time Correction → Standard Time
Therefore, you will likely need to adjust the Local Mean Time (LMT); normally displayed by a corrected analemmatic sundial like a heliochronometer, to show actual Standard (clock) Time. The reason for this is that sundial readings without longitudinal correction are only accurate if the sundial is located exactly on the meridian for the time zone it is in. A standard time zone is 15 degrees in longitude wide for every hour; i.e. 1 earth rotation every 24 hours, or 360°/24 hrs = 15°/hr, or 4 minutes for every degree of longitude. Time zones are centered on meridians; i.e. -7.5° ← (Meridian) → +7.5°. Therefore, sundials situated at the extreme eastern portion of a time zone would read as much as 7.5° x 4min/deg = 30 minutes fast, as compared to a regular clock. Conversely, sundials at the extreme western portion would read as much as 30 minutes slow. This highlights the importance of having the ability to compensate for meridian offsets if you want your sundial to accurately display actual clock time.
Here is a simple example of how to convert Local Mean Time to Standard Time (or vice versa) for a sundial situated in Vancouver, BC, Canada. Note that your dial plate only needs to be set once for your location to adjust for Standard Time.
Vancouver BC: Longitude -123° 07m; which is 3° 7m West of the Pacific Standard Time (PST) zone meridian at 120°. Therefore, the time correction (TC) would be:
TC = (3 + 7/60) x 4m/deg = 12.467m or 12m 28s.
Since Vancouver is West of the PST time zone meridian: LMT = PST - TC
or conversely: PST = LMT + TC
In this example, sundials in Vancouver would be running behind sundials situated on the Pacific Standard Time meridian. Therefore, the vernier would need to be moved counter-clockwise; i.e. ahead from it’s time zone meridian mark by 12-1/2 minutes to properly read PST. Note that every minor tick mark on the main dial is 5 minutes, so the rotation would be 2-½ minor ticks ahead on the dial. The adjustments are highlighted in the figures below:
Figure 2: Dial on Meridian (left). Dial adjusted for PST in Vancouver; i.e. LMT+ 12-1/2 mins (right)
Please note that this version of sundial cannot be adjusted to display daylight savings time.
How does the heliochronometer actually tell time?
To compute standard time, the heliochronometer makes use of several pieces of information: the observer’s latitude and longitude, the hour angle of the sun, the direction of true north, the month of the year, the declination of the su,n and an astronomical formula called the Equation of Time (EOT).
What is The Equation of Time? The Equation of Time (EOT) is the difference between true or apparent solar time and mean solar time over the course of a year. The difference in time is due to two effects: the eccentricity of the Earth’s orbit and the obliquity or tilt of the Earth’s rotational axis.
• Eccentricity of Earth’s Orbit: The Earth’s orbit around the sun is not a perfect circle but an ellipse. This means the Earth’s orbital speed varies throughout the year, moving faster when it is closer to the Sun (perihelion) and slower when it is farther (aphelion). Due to this variation in speed, the apparent movement of the Sun across the sky does not occur at a constant rate when measured against a uniformly ticking clock. When the Earth is moving faster in its orbit, the solar day (the time from one solar noon to the next) is slightly longer than the average, and when the Earth is moving more slowly, the solar day is slightly shorter.
• Axial Tilt of the Earth: The Earth’s axis is tilted at an angle of about 23.5 degrees relative to the plane of its orbit around the Sun. This tilt causes the Sun’s apparent path in the sky (the ecliptic) to be inclined relative to the celestial equator. As a result, the rate at which the Sun appears to move along the celestial equator varies throughout the year. When the Sun’s path makes a steep angle with the equator (as during the solstices), its apparent eastward motion along the equator is slower than average. Conversely, when this path is more parallel to the equator (as during the equinoxes), its apparent motion is faster. As mentioned, these two combined effects result in a discrepancy between true or apparent solar time and mean solar time. The EOT is a way of quantifying this discrepancy. It varies throughout the year, typically ranging between about -14 and +16 minutes. It reaches its maximum and minimum values around the times of the summer and winter solstices and is zero near the spring and autumn equinoxes. This discrepancy is why a sundial will sometimes run ahead of a clock and at other times fall behind it, and why the length of a true solar day is not exactly 24 hours all year round. The EOT corrects for these variations, allowing us to reconcile solar time with the 24-hour clock used in daily life.
If you think this is a cool design, don't forget to hit the like button. I hope you enjoy building this design & thanks for your support!
References:
Sundials - Their Construction & Use, R. Newton Mayall & Margaret Mayall, Dover Publications Inc., 1994
The Equation of Time: The Equation of Time
License:
Creative Commons — Attribution — Noncommercial — Share Alike
3DMason
