you should consider it as a ratio of available npk as it doesnt really provide any relavent info to the strength once diluted or mixed according to the directions, and 1-2.5-2.5 is equivalent to 10-25-25 and the lower strength 1-2.5-2.5 could just as easily have a higher or lower ppm than the 10-25-25 when diluted following the directions, but if you are using a meter to begin with you should be able to obtain similiar ppm from both fertilizers.