A game I recently started playing in inspired me to mull over the various rules on targeting systems and to consolidate them into a coherent whole for Hidden Suns. This is a topic which frequently comes up in GURPS circles and the rules have been gradually clarified I even dare say corrected during a course of several supplements.
It all started with Ultra-Tech and the HUD link, which was listed as giving +1 to Acc within 300 yards, not cumulative with other targeting systems. A multispectral laser sight, however, gave +1 to skill out to the weapon’s 1/2D range. There were two scopes, the compact and enhanced targeting scope, the former granting +2 to Acc at TL9-10 and the latter +3. This increased up to +3 and +4 respectively at TL11, and to +4 and +5 at TL12. Finally, targeting software could grant +1 or +2 to skill. Were laser sights cumulative with HUDs and scopes? No word on that, so an implied yes.
Then High-Tech came along, with collimating and reflex sights granting +1 to skill up to 300 yards. Suspiciously similar to a HUD, both in the range limitation and the description of how they worked. Could they be used together? No word in the book, but a reality check dictated that it would make sense to either use one of those two, or an ultratech HUD, but not both (a reflex sight was actually mounted on a HUD). But the ultratech HUD, as written, was inferior.
The wording on laser sights changed so that they gave “+1 to hit”, and it was possible to use them together with telescopic sights but not with collimating and reflex sights. And with a HUD? The implied answer changed from yes to no, if we followed the above reasoning. Speaking of telescopic sights, they offered up to 32x magnification translating to a +5 Acc bonus already at TL5!
Other features High-Tech introduced include the laser rangefinder, which granted +3 to Acc by making the exact range and speed of the target known to the shooter, match-grade ammunition which increased a weapon’s Acc by +1 if it was already +4 or greater, and pistol stocks which added +1 to Acc of pistols.
Next was Tactical Shooting which introduced Precision Aiming, allowing for additional Acc bonuses for Aiming longer than the standard three turns but which couldn’t exceed the lower of the used scope’s Acc bonus or the weapon’s base Acc, and clarifying that a laser rangefinder was not the only way to claim the bonus for knowing the exact speed and location of the target, offering the example of claiming it by plotting the landmarks in a field of battle.
Finally, Tactical Shooting: Tomorrow was released in Pyramid #3-55, tying up most of the loose ends. HUDs were brought in line with collimating/reflex sights from HT, giving a +1 bonus to skill but without any range limitations. It was clarified that the laser sight bonus was not cumulative with a HUD, but a targeting laser used with a HUD would automatically act as a rangefinder providing those sweet +3 to Acc. Scopes were also “modernized”, with the enhanced targeting scope becoming redundant as a variable up to 32x or +5 to Acc magnification was included for free in the compact targeting scope.
But was the HUD bonus cumulative with a scope? No explicit answer, although it was explained that a scope actually fed its video directly into the HUD, effectively focusing the user’s field of view onto the target and bringing any magnification with it. My conclusion? If a HUD gave a +1 bonus to skill by having a crosshair on the target all by its own without zoom, then having that same crosshair there but while zoomed in through a scope was the same deal. Cumulative!
The only remaining question was which of these bonuses count against the “combined bonus from all targeting systems” which can’t exceed the weapon’s base Acc, as per B364. Kromm put that to rest in his post thereby wrapping up this topic.
In the Hidden Suns, I use all of the rules covered above in their clarified state, except match-grade ammo. I don’t really use chemical slugthrowers in the setting and didn’t want to fuss around with match-grade gauss bullets or optimized plasma cartridges. As for rangefinders, I rule that it works automatically as you take an Aim action, your smartgun electronics taking care of everything in the background.