Page 1 of 1
Posted: Mon Nov 09, 2009 1:59 pm
by DNgroundworks
Hi all just wondering wether my calculations are wrong or the sums on the drainage section are wrong (probably me)
to convert 1:4 in to a percentage i would do 1/4*100 which results in 25 so its %25 - obvious i know.
I was looking at the first page on the drainage section and it says that "1:60 or 16%......"
Going off the simple calculation that ive done - which could be wrong, would it not be 1/60*100 = 1.6% ?? instead of 16%Or am i completley wrong?
Only reason i think the input mode on a pipe laser ive just bought is in percentages rather than ratios, i havent received it yet though and i was doing some sums to save time on site.
Regards Dan
Posted: Mon Nov 09, 2009 3:32 pm
by Bob_A
I reckon you are right and there is a typo in the drainage section.
By my reckoning 16% is actually 1:6.25
Posted: Mon Nov 09, 2009 4:53 pm
by lutonlagerlout
just be careful you dont get percentages mixed up with degrees dan
i use a winkelfix for finding pitches on roofs
angle finder
they are idiot proof for finding angels (handy for me)
regards LLL 
Posted: Mon Nov 09, 2009 5:38 pm
by DNgroundworks
ahh rite but is a degree not represented with a little circle aboce the number?
So on the drainage section on this site, were it states 1:60 = 16% is that 16 percent fall or 16 degrees?
Posted: Mon Nov 09, 2009 5:39 pm
by DNgroundworks
Also on the screen of the laser, it is represented as x% and not the degree sign so maybe it is percent?
Im getting good at confusing myself lol:p
Posted: Mon Nov 09, 2009 7:23 pm
by sjs
hi all, newbie so bare with me. have bin spyin on you lot for a while tho
dn your laser will deffo work in a percentage thats standard fare. and your workin out seems spot on to me mate.
ste
Posted: Mon Nov 09, 2009 8:04 pm
by cookiewales
keep up the good allways room for some more brains and daft uns
Posted: Mon Nov 09, 2009 8:12 pm
by Injured
LLL, How many 'ANGELS' does it find for you?? or did you mean angles??
Just wondering cos I could do with a couple of angels myself lol :p
Posted: Mon Nov 09, 2009 9:11 pm
by lutonlagerlout
well spotted injured
looks like i am having a *blonde* day
1:60 to me is having 1 metre rise or fall for every 60 m horizontally
i use a dumpy every week and it quite easy in practise
sort of....
LLL 
Posted: Mon Nov 09, 2009 9:48 pm
by GB_Groundworks
i'm blonde 
then again you might be right haha
Dan, is it one of those bore lasers that fits into the middle of the pipe and you line the next section up of that?
we use an automatic(dumpy) level and work out manually or use a dual grade laser, i find the leica automatic the quickest and easiest to use though.
googles a pretty good calculator you know
if you type in like "2 foot in cm" it gives you the answer
or "15lbs in kg"
not sure it does ratios though
http://www.google.com/intl/en/help/features.html#calculator
gi
Posted: Tue Nov 10, 2009 2:58 pm
by Tony McC
Can someone give me a URL for the error? I'll take a look at it and get it fixed.......
Posted: Tue Nov 10, 2009 3:29 pm
by DNgroundworks
erm i would but i dont know how! i just know it as the first page of the drainage section
Posted: Tue Nov 10, 2009 3:43 pm
by Bob_A
I think this is it
http://www.pavingexpert.com/drainage.htm
Scroll down half way down the page to the writing by the pink triangle.
Posted: Tue Nov 10, 2009 7:15 pm
by Tony McC
OK: found it.
It's more of an unfortunate juxtaposition rather than a genuine error. The text runs thus....
Gradients are expressed in a number of ways, including Ratios [1 in 60 or 1:60] and Percentages [16%]
...which I intended to provide examples of the various ways of expressing gradients. It should not be read that 1:60 *is the same as* 16%.
I should have thought more about the potential for confusion that arises from using the same numerals in that sentence. I'll change the text to make it a little clearer.
Posted: Tue Nov 10, 2009 7:23 pm
by Tony McC
Anyway, back to the original problem, of how to convert between percentages and ratios.
Let's say the gradient is given as a percentage and completely out of the air, I'll pluck the value 16%
If I put "16" into the old calculator, and then press the 1/x (inverse) button, this returns the value 0.0625, which is multiplied by 100 to remove the 'per cent', and so becomes 6.25 which in ratio terms is 1 in 6.25. The 1/x button acts to divide 1 by whatever value has been entered, so in this example, 16 INV becomes 1 ÷ 16.
To go t'other way, from ratio to percentage, simply input the ratio denominator (the big number) and press 1/x (or perform the calculation 1 ÷ denominator) and this returns the value, 0.16 which is 16 parts per hundred or, as we more commonly say, 16%.
Simples!
Afterthought: some calculators use the notation X¯¹ (x to the minus 1) rather than 1/x. It's the same thing
Edited By Tony McC on 1257881449
then again you might be right haha