# [Tutor] specifying precision with scientific notation

Alan Gauld alan.gauld at btinternet.com
Wed Oct 6 00:43:19 CEST 2010

```"Andre' Walker-Loud" <walksloud at gmail.com> wrote

>> a = 0.00762921383941
>> ea = 0.000830132912068
>> a / ea
> 9.190352205653852
>
> By default, I will print the uncertainty ("ea") with two significant
> digits.
> In this example, the central value is about 10 times larger than the
> uncertainty, so I want to print it with 3 significant figures.

I don't understand why the difference but if the deciding factor is
related
to the ratio why bother with all the string stuff? Just use the ratio
directly...

>> p = int(("%.1e" % (a / ea)).split('e')[-1]) # grab the power in the
>> scientific notation (is there a better way?)
>> if p >= 0:

Why not just

limit = 10
n = 3 if a/ea <= limit else n = 2 # or whatever expression is needed
to calculate n
fmt = "%.%de + %.1e" % n  else:

print fmt % (a, ea)

But I suspect I'm missing something in your reasoning about what size
of n you want.

--
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/

```