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Equalising anchors correctly reduces the potential load on each anchor by distributing the weight. This is a very useful tool, making two equalised anchors far superior too two anchors set in series. Two anchors that by themselves may not hold much of a fall, when combined correctly may well be stronger.

However, when equalising anchors you should NOT spread them too far apart or the concept of equalisation will actually work against you rather than for you. The diagram below shows that the reliability of the anchors decreases the wider they are spread apart. 

Below: An 80kg load clipped to two equalised anchors. (Source AMGA 1992 manual).

40kgs	40kgs	43.2kgs	43.2kgs	56kgs	56kgs	80kgs	80kgs
50% Load on each anchor		54% load on each anchor		70% load on each anchor		100% load on each anchor

With the anchors set 160 degrees apart the load on each anchor jumps to 290% meaning that in the above example of an 80kg load, each anchor is actually taking a huge 232kgs! Also with widely spread anchors, slung in the fashion shown above, you are loading the carabiner poorly. I believe the term is tri-axle loading. As a general rule, try not to spread your anchors wider than 90 degrees. 

Equalising Two Anchors With The Rope

When leading, and equalising anchors at a belay I recommend using a cordelette. If you do use the rope, consider such knots as the In-line Figure Eight, which can be easily elongated to balance the load. Or check out the Bunny Ears. For top roping I suggest a 25m length of static rope (say 11mm), rather than a cordelette, because it will be more durable in the long term.

Right: Two anchors equalised with the rope. The first anchor is tied off with a figure eight on a bite, while the second anchor is clipped to an In-line Figure Eight, whose protruding loop has been easily adjusted to equalise tension of the load between both anchors.

Equalising Two Anchors With A Sling

	Step 1: Clip the anchors with a large sling. You could clip a carabiner to your load, through both strands of this set up, but what would happen if one anchor failed? The result would be total failure. Also Note: Avoid using the "Death Triangle" pictured right. Rather than distributing the load this actually puts a greater force on the system due to the same "wide spread" principle as explained above.
	Step 2: Far better to put a twist in one strand. Step 3: And clip the load to both strands as shown. You can move the carabiner horizontally at will to adjust it to the best postion. This way should one anchor fail the system would still be in contact with the other anchor. However it would extend a great deal, badly shock loading the remaining anchor. And what if the sling itself tore? The whole system would fail. Called the "Sliding X", this is set up is not recommended in most situations, instead, continue to step four below.
	Step 4: One way to solve the problem is to instead put an overhand knot in the sling strands, and clip this to the load as shown. This way if one anchor fails, or the sling tears above the knot, then the second anchor will be loaded with little or no extension. This is not the only way to equalise two anchors with a sling.

Further Reading:
Anchor Principles -  From the university of Oregon web site.
Should I Use The Sliding X - From Dawn's Trad Girl FAQ.

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