Capricorn: Dec.22-Jan.29 The Sundial Primer
created by Carl Sabanski
Capricorn: Dec.22-Jan.29

The Sundial Primer Index

Dialling with QBASIC - Mac Oglesby - Hours to Sunset Card Sundial

"I think it would be fair to say that my involvement with card dials began with remarks by William Maddux and with programs he shared with me. In July, 1997 Bill sent me, as a surprise, the standard time card dial pictured in the attached jpg. He had written a QB program which plotted points on his computer screen and he was able to print out the screen. By hand, he "connected the dots" and wrote the labels. Not visible in the photo are the pinholes and target screens used to align the dial with the sun and located in the left and right top black tabs. The reverse side of the dial has hour lines (and date arcs) for the other half of the year. He describes this type of dial in his Compendium article "A Card Dial For Standard Time" vol. 5-1, March 1998.

Without going into boring detail, during the following months numerous emails were exchanged between myself, Bill Maddux, Warren Thom, and Fer de Vries, chatting, among other things, about methods of turning QB output into a physical dial face. Fer provided the key with his program CNVXXXX.EXE, which converts a text file into a dxf file. That program greatly expanded my ability to create sundial designs. It changed my dialing career, for sure, as many of my sundials since have flowed along the QBASIC -- CNVXXXX.EXE -- DeltaCad highway.

The team of Maddux, Oglesby, Thom, and de Vries generated several Compendium articles, the first of which was "A Card Dial With Italian Hours" in vol. 5-3 September 1998. Although four names are listed as authors, it would be fair to say that Fer de Vries was the main author, and that the original question about making card dials showing Italian hours came from Warren Thom. A card dial QB program was published with that issue, CARDDIAL.BAS and CARDDIAL.EXE (that looks like two, but they're really the same). My QB program CD-BEAD4.BAS has slightly different coding, but the important difference is that if you choose to print both AM and PM on the same side of the dates, the AM lines are beaded."

Figure 1 shows an example of a sundial that can be made. This sundial is a portable sundial but it is not universal. The sundial is deigned for a specific latitude and is used to tell how hours remain until sunset. Mac has named these type of sundials as "H2SS" or "Hours To Sunset".

Figure 1: Hours to Sunset Sundial

Figure 1: Hours to Sunset (H2SS) Sundial

Hours to Sunset Sundial - CD-BEAD4.bas

This program is called a "Horizontal Monofilar Sundial". Monofilar refers to the fact that a single piece of string is used for the shadow casting edge or style. The curved lines are the "unfolded" analemma and allow for the correction of the Equation of Time. The circular "date arcs" indicate where to read the shadow to get the correct EoT correction. The hour lines can also be corrected for longitude.

You can get the QBASIC program here.

Figure 2 shows the program when it is opened in QBASIC. Take the time to read through the comments. There is only one parameter that needs to changed if you like and is highlighted by the red rectangle and is located on line 78.

OPEN "c:\" + filename$ +

When the program is run it asks for a filename to be supplied .but it automatically writes the file to the root directory "c:" defines the disk and is likely not going to change. The path is set to the root but should be changed to a more appropriate directory. Remember to use the backslash "\".

Figure 2: H2SS Sundial QBASIC Program

Figure 2: H2SS Sundial QBASIC Program

"This program prints the dial face for a card sundial which shows Italian hours within the range of latitudes N 66.5 to S 66.5.

NOTE: Have a little patience. The program may seem to hang up when it is not. Wait for the words "Press any key to continue."."

When the program is run a number of entries must be made to give the program the design parameters to be used when drawing the sundial. The screen you will see upon completing the entries is shown in Figure 3. This information displayed on this screen will vary depending upon the answers you provide to some pf the questions. The sundial configuration can be checked at this point. If there is an error complete running the program and then start again to make any necessary changes. The sundial can be designed in a variety of ways. The best way to visualize the variations is to run them in the program.

Figure 3: H2SS Sundial Configuration Screen

Figure 3: H2SS Sundial Configuration Screen

After the program run is complete the sundial is drawn on the screen as shown in Figure 4 . The notes on the screen are not saved in the text file and should be read before exiting.

Figure 4: H2SS Sundial - QBASIC Screen Output

Figure 4: H2SS Sundial - QBASIC Screen Output

After the text file is created use the program CNVxxxx to convert it to a DXF file. Figure 5 shows the sundial when the drawing is opened in DeltaCad. Note the small cross on the upper left. This is the origin (0,0) of the drawing and is inserted by CNVxxxx.

Figure 5: H2SS Sundial DXF File Opened in DeltaCad

Figure 5: H2SS Sundial DXF File Opened in DeltaCad

Before going into the details of completing the sundial the following instructions on how to use the sundial are given in Figure 1. The will be helpful in understanding the sundial's design.

"Remove the plumb weight from its pocket. With the string taut, slide the marker bead to the date. Decide if the sun is before noon (rising), or after noon (descending). Hold the card vertical with its top right hand corner toward the sun. The string must hang freely, but against the card. Make sure the cover is out of the way. When the sunbeam through the hole in the front sight is exactly centered on the dot in the rear sight, the marker bead  indicates hours until sunset. For easy reading, pinch the string against the card while the card is properly aimed. At the design latitude, this sundial accurately gives time until sunset, but not clock time. No corrections are needed, even for daylight time. For any date, time (in hours) between sunrise and sunset is read where the centerline of the dates compartment meets the beaded lines."

Figure 6 shows a close up of the sundial in Figure 1 to illustrate the details. The pocket for the plumb weight, which can be a small flat metal disc, is visible in the bottom left of Figure 1. The marker bead is a small cylinder that fits tightly around the string so it will move when set in position. The string is set where the horizontal and vertical lines intersect. The front and rear sights are small blocks of wood. The front sight has a tiny hole drilled through its centre point parallel to the horizontal line and the back sight has a dot placed on its centre point. The hole and the dot must be aligned with one another and be parallel to the horizontal line.

Figure 6: H2SS Sundial Details

Figure 6: H2SS Sundial Details

Figure 6 shows how the hour lines are numbered and the date scale is labelled. Figure 4 has the note "Lower solstice is Dec 21" to indicate that December is at the bottom of the date scale because this sundial is designed for the Northern Hemisphere. For the Southern Hemisphere the note would state "Lower solstice is  Jun 21". If both morning and afternoon lines are shown on the card as in Figure 7, the morning lines are beaded and the afternoon lines are dashed.