Time Development Points
Time Development Points (TDPs) are used to increase attributes (mental and physical stats such as strength, intelligence, agility, and so on), as well as for other things such as buying new spell slots and forgetting learned spells.
In order to use TDP's to raise a stat, one must go to a designated room for training that particular stat and type TRAIN, then STUDY to confirm. Training rooms for each stat are available within or near every major city.
A new character is given 600 TDPs right out of the Character Manager. After that, the only way to gain more TDPs is by circling or obtaining new ranks in skills.
Each time you circle, you gain 100 TDP's plus a number equal to the circle you just gained. For example, you level up to attain circle 27. You get 127 TDP's.
Each time you gain a new rank in any skill, the integer value of that rank is added into a hidden pool (the TDP pool). If at any time the total in the pool reaches or exceeds 200, you gain one TDP and 200 is subtracted from the pool. This also applies for multiples of 200--if the TDP pool reaches 400, you gain two TDP's and 400 points are subtracted; for 600 you get three TDP's and 600 is deducted from the pool, etc.
For example, let's assume that your TDP pool is currently zero. You increase your Perception skill to attain rank 150. 150 points are added to the TDP pool. You then increase your Leather Armor skill to rank 66. 66 points are added to the TDP pool, making a total of 216. You gain one TDP, and 200 points are subtracted from the TDP pool leaving 16 points. Next, you increase your Magical Devices skill to 197. Your pool increases to 213, you gain yet another TDP, and the pool is reduced to 13.
Note that when you lose ranks from memory decay as a result of death without rejuvenation, your TDP pool will be reduced by the ranks you lost, and if this sends the TDP pool below zero you will lose a TDP, and 200 will be added to the pool. This process makes it possible to have a negative number of TDP's.