diff --git a/README.md b/README.md
index ba38f84..94b02d0 100644
--- a/README.md
+++ b/README.md
@@ -2,60 +2,52 @@
 
 ib-clearance is a program which helps schools manage the entrance and exiting of their IB students. Due to the unique nature of IB students' timetables, the program helps check individual timetables and give clearance to students who have finished for the day.
 
-### Building
+## Building
 
 The code is currently designed to run on Python 3.6.*.
 
 I recommend building executables with `pyinstaller` with `pyinstaller --onefile ib-clearance.py`.
 
-### Lesson IDs
+## Database specification
 
-Equivalents of lesson names for use in class databases.
+The program requires sqlite databases for each class.
 
-- Academic Writing
-    - 'aw'
-- Biology
-    - 'bi'
-- Business Management
-    - 'bm'
-- Chemistry
-    - 'ch'
-- Computer Science
-    - 'cs'
-- Economics
-    - 'ec'
-- English A
-    - 'ena'
-- English B
-    - 'enb'
-- French
-    - 'fr'
-- Geography
-    - 'ge'
-- German
-    - 'de'
-- Guidance
-    - 'gu'
-- Mathematical Studies
-    - 'mst'
-- Mathematics HL
-    - 'mhl'
-- Mathematics SL
-    - 'msl'
-- Polish A
-    - 'pl'
-- Psychology
-    - 'ps'
-- Self-Taught Language A
-    - 'st'
-- Spanish
-    - 'es'
-- Theory of Knowledge
-    - 'tok'
-- Turkish A
-    - 'tr'
-- Visual Arts
-    - 'va'
+Each database must contain:
+
+| Table       | Description                                                |
+| ----------- | ---------------------------------------------------------- |
+| `students`  | Contains students' names, ID numbers and class preferences |
+| `timetable` | Timetable information for class                            |
+
+### `students`
+
+| Column | Data type | Description                       |
+| ------ | --------- | --------------------------------- |
+| `id`   | `INTEGER` | Student ID number used in program |
+| `g1`   | `TEXT`    | Group 1 subject ID                |
+| `g2`   | `TEXT`    | Group 2 subject ID                |
+| `g3`   | `TEXT`    | Group 3 subject ID                |
+| `g4`   | `TEXT`    | Group 4 subject ID                |
+| `g5`   | `TEXT`    | Group 5 subject ID                |
+| `g6`   | `TEXT`    | Group 6 subject ID                |
+| `name` | `TEXT`    | Full name of student              |
+
+### `timetable`
+
+| Column      | Data type | Description                                   |
+| ----------- | --------- | --------------------------------------------- |
+| `day`       | `TEXT`    | Day of the week (e.g. `monday`)               |
+| `end_time`  | `TEXT`    | Ending time of lesson (e.g. `09:55`, `13:05`) |
+| `lesson_id` | `TEXT`    | Subject ID of the lesson (e.g. `ena`)         |
+
+#### Subject IDs
+
+Subject IDs may be anything, as long as consistency is maintained throughout the tables. There are two hard-coded IDs that are always taken by every student:
+
+| Subject             | ID    |
+| ------------------- | ----- |
+| Theory of Knowledge | `tok` |
+| Guidance            | `gu`  |
 
 ## License
 
diff --git a/ib-clearance.py b/ib-clearance.py
index f98425a..6404449 100755
--- a/ib-clearance.py
+++ b/ib-clearance.py
@@ -72,7 +72,7 @@ def select_final_time(conn, day, id):
                 OR g5 = lesson_id
                 OR g6 = lesson_id
                 OR lesson_id = 'gu'
-                OR lesson_id = 'to'
+                OR lesson_id = 'tok'
         WHERE id = ? AND day = ?
         ORDER BY end_time DESC
         LIMIT 1