This article is from the Fencing FAQ, by Morgan Burke with numerous contributions by others.
The scoring apparatus consists of the reels, floor wires, and
indicator box, and optionally a timer and scoring tower(s).
As of February 1, 2000, the scoring lamps indicate who scored the
touch. Older scoring boxes are wired to indicate who received
the touch. Reversing the cables on older boxes will cause them
to function in the new manner.
Modern foil scoring boxes should display only a coloured light or
a white light for each fencer. Older boxes (or ones with older
firmware) may display both if an off-target touch is immediately
followed by an on-target touch. Modern sabre scoring boxes
should tolerate sabres without capteur sensors. Older boxes will
display white lights with capteurless sabres, unless the sensor
leads are shorted on the weapon.
It is possible to defeat older foil scoring circuits by grounding
your own weapon to your lame' (your opponent's touches will fail
to register, but yours will register). This is illegal, and
scoring boxes must be equipped with a grounding light to detect
when fencers do this. Newer boxes have an anti-fraud feature to
eliminate this hazard and allow touches to be scored in spite of
grounding. Boxes without such an anti-fraud circuit are useful
for detecting dead spots on lame's (ground the lame', and then
touch the opponent's lame'; white lights indicate a dead spot).
Reels are typically portable, spring-wound devices (either
"turtles" or "snails"). Less portable (but often more reliable)
systems involving pulleys and bungee cords are used at some
salles. These systems require firm anchor points at the ends and
middle of the piste, so are not as portable as reel systems.