Do we reduce hindrances gradually? Do we reduce hindrances gradually ?  is it like we have 10000 units of hindrances (of different types)  and we lower them each time we are aware of them ?  

is it a right way to see how we advance - as how much we lowered our hindrances ?
The mind when covered with the five hindrances is like clouding a clear bowl of water (still mind) with different contaminants or situations. – Sangarava sutta (SN 46.55) Also try to refer to Nivaranapahna Vagga. (The 5 mental hindrances: their causes and ending – A 1.2).

The five mental hindrances (nivarana) which obstruct concentration, are: (1) sense-desire, (2) ill-will, (3) sloth and torpor, (4) agitation and remorse, (5) skeptical doubt. For details, see The Five Mental Hindrances and their Conquest, by Nyanaponika Thera (BPS Wheel No. 26).

In the Samyutta Nikaya (Sutta 46.4.8), it is stated that when one listens to the Dhamma attentively, the five hindrances (nivarana) do not exist and the seven factors of enlightenment (bojjhanga) are present. Through factors of concentration these five are suppressed (also when wholesome activities are done these five hindrances can be suppressed).


One 'pointedness' opposite of sense desires 
Joy opposite of ill will 
Discursive (applied) thoughts opposite of sloth &amp; torpor 
Happiness or comfort (pali term 'sukha') opposite of restless &amp; worry 
Sustained thought opposite of doubt 


A person becomes mindful about:


Existence of a hindrance (sense desire, ill will, sloth &amp; torpor, restlessness &amp; worry, or doubt) 
Non-existence of a hindrance 
When a non existing hindrance arises 
When a hindrance that has arisen is removed 
When the removed hindrance does not arise again


This widespread harmful influence of the five hindrances shows the urgent necessity of breaking down their power by constant effort. One should not believe it sufficient to turn one's attention to the hindrances only at the moment when one sits down for meditation. Such last-minute effort in suppressing the hindrances will rarely be successful unless helped by previous endeavour during one's ordinary life. 

One should carefully observe how, and on which occasions, these hindrances usually appear. One should further know the positive forces within one's own mind by which each of these hindrances can best be countered and, finally, conquered; and one should also examine one's life for any opportunity of developing qualities to counter these. In some cases, subjects of meditation have been added which will be helpful in overcoming the respective hindrances.

By the "worldling" (puthujjana)  however, only a temporary suspension and partial weakening of the hindrances can be attained. Their final and complete eradication takes place on the stages of sanctity (ariyamagga):


Doubt is eliminated on the first stage, the path of stream-entry (sotapatti-magga). 
Sensual desire, ill will and remorse are eliminated on the third stage, the path of non-returner (anagami-magga) 
Sloth and torpor and restlessness are eradicated on the path of Arahatship (arahatta-magga). 


Hence the reward of the fight against the hindrances is not only the limited one of making possible a shorter or longer spell of meditation, but every step in weakening these hindrances takes us nearer to the stages of sanctity where deliverance from these hindrances is unshakable.