Ph Question

[BigWilley]

When taking Ph readings at room temperature I have read that you need to subtract .3 to get the true Ph at mash temp. So a 5.5 reading at room temp would mean aprox. a 5.2 mash Ph. Can anyone verify this or shed some light? Are the reccomended Ph levels for mashing say 5.3 relative to actual Ph at mash temp or Ph at room temp? I am assuming all reccomended Ph levels are given relative to actual mash, kettle, sparge temps.

[matt]

Most pH metres are calibrated at a specified Temperature, i.g. 20 degress C. Any pH readings should have the sample as close to this temperature as possible. If the temperature is higher, pH reading is going to be lower then actual and vice versa, Temperature lower, pH reading is higher then actual.