That's a good link but I do have one issue with some of the info they have posted.
A glow plugs "heat" range has nothing to do with temperate. For example they list the MC-59, 8, and 9 all for 20-40% nitro and just varying outside temperatures. That is basically false.
The heat range of a plug is used to alter the engines timing. A hot plug advances, a cold plug retards. High compression and high nitro will both advance timing, that is why a cold plug is generally used in this condition.