WINDOW PARTS: ORIGINAL DIAGRAM LEGENDS AND READING RECORD
Learning schematics only; no dimensions, connections or installation specification.

MAIN ELEVATION
1. Mullion: main vertical division between larger lights.
2. Transom member: main horizontal division between upper and lower lights.
3. Muntins: smaller pane-dividing bars within the lower-left sash.
Four large lights; lower-left sash has four panes; other lights each have one pane.
Specified pane count: 4 + 1 + 1 + 1 = 7.

DOOR ELEVATION
1. Horizontal transom member between the door and upper glazing.
2. Transom window above the door; opening operation is not specified.

BLANK OBSERVATION RECORD
Document / photo / drawing reference:
Part location and direction:
What it divides (larger units, sash panes, or another part):
Glazing construction actually specified:
Term used in this document:
Source / glossary definition:
Different term in another document:
What remains unknown and which detail would clarify it:

SIX ORIGINAL PRACTICE CASES
1. A thin vertical strip divides two panes inside one sash. In the terminology of this guide, is its vertical direction enough to call it a mullion?
Your label and reason:

2. In the main elevation, four large lights are shown. The lower-left sash has four panes and each of the other three lights has one. How many panes are specified?
Your label and reason:

3. A caption says “the transom window above the door.” Does it mean only the horizontal bar separating the door from the glazing?
Your label and reason:

4. You see a horizontal line at the lock where the upper and lower sashes of a double-hung window meet. Must it be a transom?
Your label and reason:

5. A drawing explicitly labels a decorative grid over one continuous pane. The grid looks like six small rectangles. Can you report six separate panes?
Your label and reason:

6. A Scottish institutional glossary names vertical stone bars mullions. A Kentucky restoration glossary uses mullion for a structural muntin spanning a sash. Should you choose a country and assume every document there follows one definition?
Your label and reason:

ANSWERS AND REASONS
1. No. It is a pane-dividing muntin in the stated sash.
Start with what the strip divides: individual panes within the sash, rather than the larger window units or lights. A muntin can run vertically, so a rule that equates every vertical line with a mullion would mislabel this example. If you are reading a supplier’s drawing that uses a different label, record that label alongside its actual role instead of silently changing the document.

2. Seven panes in four large lights.
Count the four panes in the divided lower-left sash, then add one for each of the other three lights: 4 + 1 + 1 + 1 = 7. Counting only the larger mullion-and-transom divisions would give the number of lights, not all the individual panes in this schematic. This count follows the stated construction of the teaching drawing; a surface grid in a photograph would need more information before you used the same method.

3. No. Here the noun phrase names the upper window.
Merriam-Webster records both the architectural crossbar and the window above a door or another window. The phrase “transom window” identifies the glazed unit in this caption. The supporting or separating crossbar is the transom member. Keeping those two referents separate helps you follow an annotation or a specification. Do not add an opening direction to your notes unless the actual drawing or description supplies it.

4. No. Identify the meeting rails of the two sashes first.
The restoration glossary describes the meeting rail at the upper edge of the lower sash and lower edge of the upper sash. It also defines rails as the horizontal frame parts of a sash. The location and relationship between the two sashes explain the line more precisely than orientation alone. A separate crossbar can exist elsewhere in a window; this particular clue is the sash meeting, not evidence that every horizontal frame edge has the same name.

5. No. Record one continuous pane with a decorative grid.
The stated glass construction is one pane. A surface pattern does not change that fact. Some supplier vocabulary uses muntin for a decorative sash element, so the product’s chosen word need not establish separate glass pieces. Your note can preserve both facts: “Decorative grid, called muntins in this document; one continuous pane is specified.” That is clearer than inferring pane count, glazing retention or load capacity from the pattern alone.

6. No. Match each definition to the source and the part being described.
The examples show that vocabulary depends on the architectural setting and the particular author or trade source. They do not survey every British or American practice. Record the larger window division, sash member or pane divider actually described, then quote the document’s label. If that role remains ambiguous, ask which component the annotation points to. A regional assumption would not resolve a missing detail or a supplier-specific definition.

Keep the component’s role and the source’s label together. These source examples do not establish a rule for every British or American document.
Sources:
https://mackintosh-architecture.gla.ac.uk/catalogue/glossary/?gid=glos-multran&xml=des
https://www.merriam-webster.com/dictionary/muntin
https://www.merriam-webster.com/dictionary/transom
https://heritagewindowsolutions.com/window-restoration-glossary/
https://www.tvwindows.com/window-mullions-and-transoms/