IET On-Site Guide Appendix E (Tables E5/E6, the 45% space factor rule with the major-axis definition); ESC Technical Manual T113-1 and T113-3 (cable factors extended to 240 mm2, spare capacity rule, internal areas); BS 7671 (521.5.1, 521.7, 521.10.1, 521.10.202, 527.2.2, 528.1, Appendix 4 Reference Method B and Table 4C1); BS 5839-1:2025 35.5, BS 5266-1:2025 8.2.6, BS 8519 cl.15/16 and Annex B; Legrand Salamandre 2019 standard range; MK PVCu 45% areas; BS 7629-1 and Prysmian FP200 Gold dimensions; OSG Table D4 supports; Quelfire tested firestop details.

16/09/2026 (1.3.8): the wording in the tool was revised in plain UK English. The compliance record line and the How this works list now say in the tool, and the segregation and compartment checks are called checks. The calculations, the printed report and the exports are unchanged. The 1,538 scenarios in each tier, the derived-input check and the term-of-art check were re-run on 1.3.8 with no findings; verified live after upload. 15/09/2026 (1.3.7): the notes written inside the program code were rewritten in plain UK English. The calculations, the wording shown in the tool, the printed report and the exports are unchanged. The 1,538 scenarios in each tier were re-run on 1.3.7 with no findings; verified live after upload. 15/09/2026 (1.3.5 and 1.3.6): every citation of the fire alarm and emergency lighting standards was read back against the current editions. BS 5839-1:2025 replaced the 2017 edition: the compartment rule is now cited to 35.5, non-metallic trunking to BS EN 50085-1 (35.7) and the support note to 35.3, which says non-metallic trunking as the sole means of support is likely to be precluded. BS 5266-1:2025 replaced the 2016 edition: its clause 8.2 applies to emergency lighting fed from a central power supply system, so the partition, the marking of reserved trunking and the non-combustible support are now stated for that case, and supply cables to self-contained luminaires are named as installed like a normal lighting circuit (8.1); the subscriber compliance record quotes clause 8.2.6 of the 2025 edition word for word. Two new automated checks read every citation, and the wording of every program file, in the tool, the report and the printed sheet, and fail on the 1.3.4 and 1.3.5 builds; the 1,538 scenarios, the derived-input check and the term-of-art check were re-run on 1.3.6 in both tiers with no findings; no factor, size or limit changed; verified live after upload. 11/09/2026 (1.3.4): a check across every PD tool for an input shown to every user that only a minority case reads. The storey height field was shown on every vertical section, although only a vertical section that penetrates a fire-rated element reads it, for the slab crossings in the support note. It now shows only once that box is ticked on a vertical section, and ticking the box reveals it at once. An automated check for it was added and fails on the 1.3.3 build; the 1,538 scenarios, the derived-input check and the term-of-art check were re-run on 1.3.4 in both tiers with no findings; no factor, size or limit changed; verified live after upload. 10/09/2026 (1.3.3): a check across every PD tool for a figure printed as entered that the user never gave. Every new section started with a 6 m length that was printed in the check row, the schedule and the report as if entered, and a vertical section left at it was told to provide intermediate supports for a 6 m run nobody had specified. A new section now starts with the length blank: the capacity result does not depend on it, and the support count, the pin racks and the fire-stopping positions ask for it until it is entered. An automated check now tests a fresh section in both tiers (blank field, the request line, no vertical note without a length, the note once a length is entered, blank again after Start again and on an added section) and fails on the 1.3.2 build; the 1,538 scenarios, the derived-input check and the term-of-art check were re-run on 1.3.3 with no findings; no factor, size or limit changed; verified live after upload. 04/09/2026 (1.3.2): the sizing basis is now headed How this size was reached and laid out as numbered steps for each section, with the section's size and verdict at the head of its card and every figure in bold, so the calculation behind the answer reads as a worked example for the case entered. The steps are the same calculations as before and the report shows them under the same heading. The 1,538 scenarios were re-run on 1.3.2 in both tiers with no findings; no factor, size or limit changed; verified live after upload. 04/09/2026 (1.3.1): a check of whether every input the standard names by a term of art is defined in the tool, printed back and questioned where a wrong entry can be seen. The custom internal width and depth fields took the catalogue size, which names trunking by its outside dimensions, so 75 x 50 entered gave 3750 mm2 where the tool's own Table E6 figure for that size is 3456 mm2; the custom cable diameter field took the conductor size in place of the overall diameter. Both now show help naming the figure meant and the entry that is wrong. A custom steel or PVCu size equal to one on the standard list, or a diameter equal to a conductor size, prints a check line with the figure the tool holds while still giving the answer; a fire-rated system, always entered by hand, is not questioned this way. The 1,538 scenarios were re-run on 1.3.1 with no findings; no factor, size or limit changed; verified live after upload. 04/09/2026: the full input range was enumerated, 1,538 scenarios in each tier: every single-core size from 1.5 to 240 mm2 in PVC and LSZH, solid and stranded, FP200 and BS 7629 multicores, ESC three-core and flat cables, mixed sets, at four quantities, three spare capacities, one and two compartments, steel and PVCu, every standard steel size checked manually, the fire-rated path with and without the manufacturer size, and blank or nonsense spare entries. The proposed size, the verdict word, the support centres against On-Site Guide Table D4, the grouping factor against BS 7671 Table 4C1 and the Table E5 and E6 figures were each recomputed independently from the source tables and compared with what the tool prints. No difference was found. 03/09/2026 (1.3.0): a check across every PD tool that every printed value is reached through the input the standard derives it from. A fire-rated system was found to be sized and passed on the steel Table E6, with its current rating printed without the BS 8519 Annex B correction: it now asks for the manufacturer's internal size and tested support centres and prints the rating rule instead of a figure. Current ratings are given only for the FP200 cable the datasheet covers, other cables are pointed to their BS 7671 Appendix 4 table. Blank spare and blank length ask for the value; circuits beyond Table 4C1 say so; compartment widths can be entered; Band I cables state whether they are insulated for 300/500 V before the Reg 528.1 note applies; the 528.1 methods are numbered 1 to 6 as the A4 text has them. The audit checks were run in both tiers; verified live after upload; no size or factor changed on steel or PVCu. 02/09/2026 (1.2.3): every cited BS 7671 clause was read back against BS 7671:2018+A4:2026, BS 5266-1:2025 and BS 5839-1:2025; the result summary names the section with the highest utilisation and the trunking cover rule is cited to Reg 530.4.3; no size or factor changed. 02/09/2026 (1.2.2): the revised wording was checked in the tool against the house style, using the FF core transition preset; no size or factor changed. 33 checks were run: both ESC worked examples (unit system and space factor), the RM Technical chart example, a real project cable schedule, and the published internal-area figures (75x50 = 3455 mm2, 75x75 = 5270 mm2, reproduced by factor / 0.45). All 37 steel factors were verified against On-Site Guide Table E6. The grouping check was verified against the FP200 Gold datasheet and Table 4C1.