If you have an iPhone or an iPad you could buy the kello application, which is a makeshift watch timing app. It does not work with some extremely quiet movements, but I've had good luck with my attempts and can get my reps to +2.5 secs a day which makes me very happy.
There are tutorials on this Forum already for timing watches but in brief, you can use the fine adjuster screw up to a point but if this is not enough you have to carefully slide the larger "tab" adjuster for more gross adjustments. My latest rep was +50 a day upon receipt, but the adjustment tab and kello brought it down to +2.5 for me.