Ok, let me be more specific on how you can tell- you have to gauge certain reactions to foods, training, sex drive, attitude, over a period of time. You can't just say I'm full of T after a workout or after sex, as you are right. But, if for a whole week you are breaking out with zits on your shoulders, your skin is oily as hell, you eat until there is no tommorrow and don't crap any of it out, you find yourself lowering your standards of women you'll have sex with, you smell sex, (and a really huge one here-) women smell way more T on you, these are some signs. This is also relative as you pointed out, these signs may mean you might have higher than your normal t-levels but not nessasarily high levels. Recovery rate and strength increases over time is another sign of raising t-levels. These signs are even easier to recognize in women though