# Question: Line of best fit? (1 Viewer)

#### SupaGloo

##### Member
Does the line of best fit have to pass through 0,0 ? ie: the origin

physics teacher sez it doesnt
chem teach sez it does
tutor sez it does
excel give an example where it doesnt...

they say it depends on whats on the axes... but then its assumption if u base it on that...

so its kinda 50/50 atm...

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"if you don't know the answer, just make it up" - Mr Singer

No, it doesn't.

#### SupaGloo

##### Member
k thx...

...but maybe i should have phrased it better

say the trend line crosses the y axis at around say 10 in a linear fasion, but u know that in reality it would pass 0,0 (eg: absorbance) BUT 0,0 isnt denoted in any table of values to plot

would u make adjustments acording to that fact u know it would anyway?

_____________________________________

"if you don't know the answer, just make it up" - Mr Singer

#### Lazarus

##### Retired
In that case, yes.

#### soz

##### New Member
okay this line of best fit stuff is this chem or phys coz i do chem and i havent done anything on 'lines of best fit'
what is it? when do i need to use it?

#### SkAnDi

##### Member
Don't extend after given data unless you lose a dotted line.

2/3 for my trial mark.

I have NEVER got complete marks in a graph before.

#### spice girl

##### magic mirror
Originally posted by SupaGloo
k thx...

...but maybe i should have phrased it better

say the trend line crosses the y axis at around say 10 in a linear fasion, but u know that in reality it would pass 0,0 (eg: absorbance) BUT 0,0 isnt denoted in any table of values to plot

would u make adjustments acording to that fact u know it would anyway?
In theory it would pass through 0,0, but in reality, even if you have a substance-free sample, the instrument won't measure 0. 0,0 is not a point on the line of best fit, i'm afraid.

Usually graphs for instruments such as AAS are only linear for a small range of values, that's why there's a limit on the min conc. it actually detects.

#### Lazarus

##### Retired
There seem to be quite a few websites that suggest including (0, 0) is the correct way to go... I know we were told to do that last year. Which is correct?

#### spice girl

##### magic mirror
For some physics graphs, yes.

For AAS calibration curves, you're not meant to plot (0,0) as a point. This is because the instrument usually doesn't read 0 absorption at 0 concentration (i.e. a blank).

#### Lazarus

##### Retired
Mmm, that makes sense - thanks.