Grand Exchange Market Watch/Index adjustments

Indices must be adapted constantly to changing conditions so they can fulfill their purpose as measuring instruments for the Grand Exchange Market Watch. This page is meant to show the calculations for the adjustments made to the indices. For more information, see Grand Exchange Market Watch/FAQ.

Common Trade Index

12 February 2012

The CTI was adjusted on 12 February 2012 with the removal of six items (Mithril ore, Law rune, Big bones, Raw swordfish, Vial of water, Clean ranarr) and the addition of 10 items (Abyssal whip, Dragon boots, Rune armour set (lg), Red chinchompa, Oak plank, Shark, Green dragonhide, Dragon bones, Cannonball, Dragonfire shield). This brought the total of items in the CTI to 27 items.

List of items and prices
Item	Base price	Price on 12-Feb-2012
Coal	159	320
Steel bar	540	1,335
Gold ore	528	304
Mithril ore	315	349
Nature rune	271	226
Death rune	299	452
Law rune	303	363
Pure essence	80	125
Yew logs	411	522
Magic logs	1,222	1,592
Cowhide	109	513
Big bones	419	621
Raw lobster	237	285
Raw swordfish	325	492
Raw monkfish	350	601
Flax	70	72
Soft clay	207	541
Limpwurt root	646	2,060
Snape grass	428	314
Vial of water	98	36
Clean ranarr	5,959	4,958
Clean snapdragon	6,885	9,866
Clean kwuarm	3,030	1,828
Abyssal whip	–	420,951
Dragon boots	–	103,701
Rune armour set (lg)	–	136,531
Red chinchompa	–	1,592
Oak plank	–	639
Shark	–	1,715
Green dragonhide	–	2,196
Dragon bones	–	3,962
Cannonball	–	407
Dragonfire shield	–	7,946,801

With the removal and addition of several items, we need a new divisor:

${div}_{\text{new}}={div}_{\text{old}}\times {\frac {\sum \left({\frac {p}{q}}\right)_{\text{new}}}{\sum \left({\frac {p}{q}}\right)_{\text{old}}}}$

And, to calculate the new divisor, we need to find:

${\begin{aligned}{div}_{\text{old}}&=21.791759207424\\\sum \left({\frac {p}{q}}\right)_{\text{old}}&={\frac {320}{159}}+{\frac {1335}{540}}+{\frac {304}{528}}+\dots +{\frac {1862}{3030}}=35.26980062\\\sum \left({\frac {p}{q}}\right)_{\text{new}}&=\sum \left({\frac {p}{q}}\right)_{\text{old}}-\left({\frac {349}{315}}+{\frac {363}{303}}+\dots +{\frac {4958}{5959}}\right)+\left({\frac {420951}{420951}}+{\frac {103701}{103701}}+\dots +{\frac {7946801}{7946801}}\right)=38.76853218\end{aligned}}$

Thus, the new divisor is:

${div}_{\text{new}}=21.791759207424\times {\frac {38.76853218}{35.26980062}}=23.9535$

See also

• Grand Exchange Market Watch/FAQ
• Template:GE Common Trade Index