Relatively insensitive film, with a correspondingly lower speed index, requires more exposure to light to produce the same image density as a more sensitive film, and is thus commonly termed a slow film. Highly sensitive films are correspondingly termed fast films. In both digital and film photography, the reduction of exposure corresponding to use of higher sensitivities generally leads to reduced image quality (via coarser film grain or higher image noise of other types). In short, the higher the sensitivity, the grainier the image will be. Ultimately sensitivity is limited by the quantum efficiency of the film or sensor. 

The Warnerke Standard Sensitometer consisted of a frame holding an opaque screen with an array of typically 25 numbered, gradually pigmented squares brought into contact with the photographic plate during a timed test exposure under a phosphorescent tablet excited before by the light of a burning Magnesium ribbon. The speed of the emulsion was then expressed in 'degrees' Warnerke (sometimes seen as Warn. or °W.) corresponding with the last number visible on the exposed plate after development and fixation. Each number represented an increase of 1/3 in speed, typical plate speeds were between 10° and 25° Warnerke at the time.
What is the speed of a insensitive film?
What does it require more of?
What is another name for it?
What is a fast film?
What is a sensitive film?
So what happens if it has higher sensitivity?
How does that do to the image?
What causes the image to be grainier?
What is sensitivity limited by?
What did the Warnerke Standard Sensitometer consist of?
What else did it have?
What did it connect with?
What was the speed expressed in?
Was there an abbreviation for it?
What did each number represent?
An increase of 1/3  represented what?
What were typical plate speeds?
lower speed
with a correspondingly lower speed index
exposure to light
requires more exposure to light
slow film.
 commonly termed a slow film. 
no
 termed a slow film
fast films
Highly sensitive films are correspondingly termed fast films
reduced image quality
generally leads to reduced image quality
via coarser film grain or higher image noise of other types
(via coarser film grain or higher image noise of other types
high sensitivity
 In short, the higher the sensitivity, the grainier the image
the quantum efficiency of the film or sensor.
Ultimately sensitivity is limited by the quantum efficiency of the film or sensor.
a frame
The Warnerke Standard Sensitometer consisted of a frame holding an opaque screen with an array of typically 25 numbered, gradually pigmented squares brought into contact with the photographic plate
an opaque screen with an array of typically 25 numbered, gradually pigmented squares
 an opaque screen with an array of typically 25 numbered, gradually pigmented squares
a photographic plate during a timed test exposure under a phosphorescent table
contact with the photographic plate during a timed test exposure under a phosphorescent table
degrees
The speed of the emulsion was then expressed in 'degrees
Warn. or °W
 Warnerke (sometimes seen as Warn. or °W
corresponding with the last number visible on the exposed plate after development and fixation.
corresponding with the last number visible on the exposed plate after development and fixation.
Each number
 Each number represented an increase of 1/3 in spee
10° and 25° Warnerke
typical plate speeds were between 10° and 25° Warnerke