RuneScape:Grand Exchange Market Watch/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.

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.

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{align}

{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} = 35.34047238 \\ \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{424800}{424800} + \frac{106700}{106700} + \dots + \frac{7900000}{7900000} \right ) = 38.83204404 \end{align}$$

Thus, the new divisor is:


 * $${div}_{\text{new}} = 21.791759207424 \times \frac{38.83204404}{35.34047238} = 23.9447$$