It's funny.. an OT test only tell you that your Lutenizing Hormone (LH) is rising.. and therefore, you "could" ovulate.in fact, just because the test may show a positive, it doesn't mean you WILL ovulate.. it simply means your body produced enough of the LH hormone to meet the test's designated threshold... how can you know IF you are truly ovulating.. you can only know that by taking your temp and charting your cycle.. oh sure, some will say, I KNOW exactly when I am. I get a sharp pain (ok , yes, at times we do) however and again.. that doesn't completely mean you are ovulating.. some say, well I bled this month... that means I did.. NO it doesn't.... it means you bled but could have had an anovulatory cycle..
those OT tests are misleading because many thing they determine if you will ovulate...again, they simply measure the LH ..those tests can help in conjunction to tracking your cycle... check out that book, take charge of your fertility..
oh and IF you insist on using the tests (which can have their place) you can buy them in bulk on the net for cheaper than if you buy them at the store.. depending upon how long you use them, costs can add up....
good luck