Many people (especially players of high level and/or high Int mages) wish to extend the Detection of Invisibility table found on p. 60 of DMG1 (p. ** of DMG2) to higher Intelligences and levels/hit dice. This is difficult to do unless you understand their structure, which is fairly complicated. The Intelligence of the creature goes in bands of decreasing width; the level at which 5% chance is reached decreases steadily at 1 level/hit die per band; the chance increases by 5% per level below Int 8 or level 9, by 10% per level below Int 15 or level 13, and by (15% plus 5% per band) per level otherwise. The extended table is thus as follows:
| Level | Hit Dice of Creature | Intelligence Ability Rating | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0–1 | 2–4 | 5–7 | 8–10 | 11–12 | 13–14 | 15–16 | 17–18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | |||
| 0 | <1 | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 5% | |
| 1 | 1 / 1+ | — | — | — | — | — | — | — | — | — | — | — | — | — | 5% | 10% | |
| 2 | 2 / 2+ | — | — | — | — | — | — | — | — | — | — | — | — | 5% | 10% | 15% | |
| 3 | 3 / 3+ | — | — | — | — | — | — | — | — | — | — | — | 5% | 10% | 15% | 20% | |
| 4 | 4 / 4+ | — | — | — | — | — | — | — | — | — | — | 5% | 10% | 15% | 20% | 25% | |
| 5 | 5 / 5+ | — | — | — | — | — | — | — | — | — | 5% | 10% | 15% | 20% | 25% | 30% | |
| 6 | 6 / 6+ | — | — | — | — | — | — | — | — | 5% | 10% | 15% | 20% | 25% | 30% | 35% | |
| 7 | 7 / 7+ | — | — | — | — | — | — | — | 5% | 10% | 15% | 20% | 25% | 30% | 35% | 40% | |
| 8 | 8 / 8+ | — | — | — | — | — | — | 5% | 10% | 15% | 20% | 25% | 30% | 35% | 40% | 45% | |
| 9 | 9 / 9+ | — | — | — | — | — | 5% | 10% | 15% | 20% | 25% | 30% | 35% | 40% | 45% | 50% | |
| 10 | 10 | — | — | — | — | 5% | 15% | 20% | 25% | 30% | 35% | 40% | 45% | 50% | 55% | 60% | |
| 11 | 10+ / 11 | — | — | — | 5% | 15% | 25% | 30% | 35% | 40% | 45% | 50% | 55% | 60% | 65% | 70% | |
| 12 | 11+ / 12 | — | — | 5% | 15% | 25% | 35% | 40% | 45% | 50% | 55% | 60% | 65% | 70% | 75% | 80% | |
| 13 | 12+ / 13 | — | 5% | 10% | 25% | 35% | 45% | 50% | 55% | 60% | 65% | 70% | 75% | 80% | 85% | 90% | |
| 14 | 13+ / 14 | 5% | 10% | 15% | 35% | 45% | 55% | 65% | 75% | 85% | 95% | 105% | 115% | 125% | 135% | 145% | |
| 15 | 14+ / 15 | 10% | 15% | 20% | 45% | 55% | 65% | 80% | 95% | 110% | 125% | 140% | 155% | 170% | 185% | 200% | |
| 16 | 15+ / 16 | 15% | 20% | 25% | 55% | 65% | 75% | 95% | 115% | 135% | 155% | 175% | 195% | 215% | 235% | 255% | |
| 17 | 16+ / 17 | 20% | 25% | 30% | 65% | 75% | 85% | 110% | 135% | 160% | 185% | 210% | 235% | 260% | 285% | 310% | |
| 18 | 17+ / 18 | 25% | 30% | 35% | 75% | 85% | 95% | 125% | 155% | 185% | 215% | 245% | 275% | 305% | 335% | 365% | |
| 19 | 18+ / 19 | 30% | 35% | 40% | 85% | 95% | 105% | 140% | 175% | 210% | 245% | 280% | 315% | 350% | 385% | 420% | |
| 20 | 19+ / 20 | 35% | 40% | 45% | 95% | 105% | 105% | 155% | 195% | 235% | 275% | 315% | 355% | 395% | 435% | 475% | |
| +1 lvl. | +1 HD | +5% | +5% | +5% | +10% | +10% | +10% | +15% | +20% | +25% | +30% | +35% | +40% | +45% | +50% | +55% | |
Note that percentage chances above 100% are significant: Improved Invisibility, for example, imposes a -25% modifier on the chance. Referees familiar with RuneQuest might wish to give a little more information if the character rolls under 1/5th, and even more if they roll under 1/20th (rounded up) of their (adjusted) chance; if so, any roll of 95+(chance over 100 rounded down) or above (or 00 if their chance is over 500%) should be a failure, and false information should be given if the character rolls 95+(chance over 20 rounded up) or above, or on a 00 unless their chance is over 500%. (Thus characters with a 5% chance spot things that aren’t there as often as they spot things that are!)