This tour covers Heinz Lemke's 1972 SYMELEC from start to finish, in the emulator at hyperties.org/cabinet/symelec. It follows his PIXIE user manual (thesis appendix 4), and every step below was checked against the running program. Each section is one take: what to do, then what to say.

Before you record

• Open the cabinet. Turn on the panels you want in shot: PLAY, TTY, RINGS and MEMORY. Shift-click a chip to show that panel alone.
• Leave the speed at 1×.
• Tap, don't hold. SYMELEC reads a button still under the pen as a second tap, so if you hold S it opens the element and closes it again.
• Drag slowly. The cross follows the pen only as fast as its search raster can find it.
• Go around lit lines, not across them. A lit line the pen passes over catches the cross.
• Memory is small: room for 35 to 50 nodes and branches. To start clean, drag RESET down or type START.

1. The screen

Say: "This is a PDP-7 with a DEC 340 display, running the program from Heinz Lemke's 1972 listing. My mouse is the light pen."

• The + is the tracking cross. It is always live to the pen, in either mode.
• The six letters around it are the control buttons. They move with the cross, so your hand is always near them: a radial menu, in 1972. They show only what is legal right now.
• The right-hand column holds the twelve command buttons: DR, HV, RU and SF for drawing; PO, AT, IN, SC, CA, RE, RO and EN for pointing.
• PIXIE sits at the lower left. Leave it alone for now (§9).
• The readout at the top right is the cross position, read live from SYMELEC's own variables.
• Hover over anything on the tube and a tooltip names it, quoting the manual.

2. Moving the cross

Press on the + and drag it somewhere empty. Nothing is drawn, because no element is open.

Say: "The cross follows the pen. Between elements it moves without ink."

3. A line: S, drag, F

1. Tap S, upper left of the cross. It turns into F: an element is open.
2. Drag. A trail of light follows. HV, the default, turns the path into horizontal and vertical steps.
3. Let go and drag again. Every release is a corner.
4. Drag back over the trail: it undraws. Corrections cost nothing until you finish.
5. Tap F. The element freezes and is compiled into the picture.

Say: "S starts a segment and F finishes it. Same button: it changes its letter."

4. Straight lines: RU

Move the cross away, tap S, then tap RU in the right column. Drag: one rubber-band line at any angle, from the start to the cross. Tap F.

The mode stays set until you tap another, so tap HV to go back to stairs. A diagonal drag in HV makes a staircase.

The program helps your aim:

• A corner closer than about 25 units to the last one is dropped.
• An end near an existing node snaps onto it.
• S or F next to a branch, but not on one of its terminals, is refused.

5. Components: R, C, L, S; A for V, I, U, O

With an element open in HV mode:

1. Draw a short wire.
2. Tap R. A resistor goes in at the cross, turned to the direction you were drawing.
3. Draw some line before the next component. A symbol needs wire on both sides, so a second component tapped straight after the first does not go in.
4. Tap C for a capacitor, draw more wire, then tap L for an inductor, or S for a switch. This S is the ring's lower-right S, not the S/F button.
5. Tap A. The ring changes to the second set: V voltage source, I current source, U nullator, O norator. B brings the first set back.
6. Tap F.

Each component gets a type number automatically, for programs on Titan to read: R 1, C 2, L 3, V 4, I 5, S 6, O 7, U 10.

Say: "Components are just part of the line you're drawing. Wire, resistor, wire, capacitor, wire."

6. Pointing mode: blink, M and L

1. Tap PO. The ring changes to C E T M L G.

2. Tap a line in the picture. Part of the picture blinks, about twice a second. At first the whole schematic blinks.

3. Tap L ("less"), then tap the line again: now only the node or branch you hit blinks. Tap L again and re-tap to go down one more level. M ("more") goes back up.

   Every button turns the blink off, so tap the picture again after M or L.

4. At the lowest level, a single line, the teletype says NOTE 6 when you try something that cannot apply to a line, such as naming it. Tap M to go up a level.

Say: "The drawing isn't pixels. It's a model, schematic, nodes, branches, lines, and M and L walk up and down it."

7. Names and data on the teletype

With something blinking, click the TTY panel and type. Each line ends with Return.

You type	It does
R1	Names the blinking instance R1. Every new instance starts with a two-digit name, 00 to 99.
/10K	Adds the line 10K to the instance's parameter data.
:RESISTOR	Sets the type of its subpicture, the prototype every copy shares.
Return on its own	Lists the name, the data and the type: R1, 10K, :RESISTOR.
? before Return	Cancels the line.

Say: "An instance has a name and data. Its subpicture, the prototype every copy points to, has a type. That's 1972 object-oriented graphics."

8. Edit: C, T, E, G, EN

With something blinking:

• T moves it: drag the cross, and the object follows at a fixed offset.
• C copies it, then you are carrying the copy.
• E erases it.
• G adds it to the current group. Blink several pieces and press G after each.
• EN ends the group and turns the blink off.

9. Your own symbols: CA, RE, RO, AT

1. Draw a shape. Blink it, at a level below the whole picture.
2. Tap CA to catalogue it as a new basic symbol. RE makes a half-size copy and RO a copy turned 90°; neither of those copies has terminals.
3. Put the cross on each terminal in turn and tap AT to make it an attachment point.

If you blink the whole schematic, CA gets NOTE 7: tap L first.

IN and SC are in the menu but were "not yet implemented" in 1972.

Tapping PIXIE at the lower left deletes the drawing-mode control buttons and IN, SC, CA, RE and RO, to free core for a bigger drawing. There is no undo except a reboot.

10. Teletype commands

These work only while nothing blinks: tap EN or DR first. The first three letters of a command are enough.

Command	Effect
LABEL	Writes every instance's name on the picture.
UNLABEL	Removes the names from the screen; the model keeps them.
GRID	Snaps drawing to an invisible grid about 0.1 inch apart. LABEL, UNLABEL or START turns it off.
TITAN	Freezes PIXIE and sends the ring structure down the link to the Cambridge Titan, here Tiny Titan. Return thaws it. Draw something first: TITAN on an empty picture crashes the 1972 program.
START	A clean start: a blank frame.

PIXIE answers ? to anything else.

11. Messages

NOTE 1, 2	Out of data-structure or display-file space. Save to Titan, or stop drawing: SYMELEC soon starts over on its own.
NOTE 3, 4, 5	Titan link errors: checksum, not PIXIE data, file too large.
NOTE 6	That command cannot apply to a single line. Tap M.
NOTE 7	That command cannot apply to the whole schematic. Tap L.
NOTE 8	The working stacks are full.

12. The rings in 3D

Open RINGS. This panel is the data structure itself, read live from core between BEG and END, starting from SAVINS. It is not the display file.

• On a blank frame the panel is empty.
• One line is about 20 cells. A wire with a resistor is about 60.
• Cells are green and blocks purple. Car pointers are blue, cdr links green, and the yellow link is where a chain closes into a ring. Cells that just changed flash white.
• Drag to turn the model, scroll to zoom, and hover to read a cell's address and words. Click a cell to open it in MEMORY.
• spin toggles the slow turn. file loads a saved ring image (YAML, JSON or a transfer stream) instead of live core.

Say: "Every stroke you draw is a few dozen list cells. This is what went down the wire to Titan."

Draw with RINGS open and the structure grows each time you tap F.

13. The program running

Open MEMORY and choose the source view: the 1972 listing, with 👉 on the line the PDP-7 is running right now. The 1972 listing, Cambridge source and as7 translation are each one line of code per row, with the scanned printout page beside it. REGS is the front panel: switches, AC, PC and device flags.

Say: "That's Heinz's code, transcribed word for word from 128 pages of lineprinter paper, running."

14. The demo, and recording

• DEMO (in PLAY) reboots and lets a scripted pen draw a house, a sun, a tree, a hedge, a circuit and a flag. Captions explain each move. Every stroke is SYMELEC's; the script only moves the pen. Afterwards memory is nearly full.
• ⏺️ reboots and records your switches, keys and pen until you press it again. 📼 replays the recording from a fresh boot. ⬇️ downloads it as JSON.

Time is counted in machine cycles, so a replay draws the same picture at any speed. A good way to film: record your session first, then replay it at 1× while the screen recorder runs.

• Copy screen copies the tube to the clipboard as a PNG. Print screen saves it as SVG.

A five-minute take

1. Screen tour (§1). Drag the cross (§2).
2. An HV wire with R, more wire, then C; tap F (§3, §5).
3. S RU, one diagonal, F (§4).
4. PO, tap the resistor, L, re-tap until only it blinks (§6).
5. Type R1, /10K, :RESISTOR, then Return to list them (§7).
6. T and move it; EN; type LABEL (§8, §10).
7. RINGS: turn it, hover over a cell (§12).
8. MEMORY source view (§13).
9. DEMO to close (§14).

More: Drawing with SYMELEC, Tracking, Tiny Titan, Bug journal, The listing, PIXIE.