Your scaling will need to take into account the possible range of the original number. There is a difference if your 200 could have been in the range [200,201] or in [0,200] or in [0,10000].

So let 

 * $r_{\text{min}}$ denote the minimum of the range of your measurement
 * $r_{\text{max}}$ denote the minimum of the range of your measurement
 * $t_{\text{min}}$ denote the minimum of the range of your desired target scaling
 * $t_{\text{max}}$ denote the minimum of the range of your desired target scaling
 * $m\in[r_{\text{min}},r_{\text{max}}]$ denote your measurement to be scaled

Then

$$ m\mapsto \frac{m-r_{\text{min}}}{r_{\text{max}}-r_{\text{min}}}\times (t_{\text{max}}-t_{\text{min}}) + t_{\text{min}}$$

will scale $m$ linearly into $[t_{\text{min}},t_{\text{max}}]$ as desired.

To go step by step,

 1. $ m\mapsto m-r_{\text{min}}$ maps $m$ to $[0,r_{\text{max}}-r_{\text{min}}]$.
 2. Next,
 $$ m\mapsto \frac{m-r_{\text{min}}}{r_{\text{max}}-r_{\text{min}}} $$

 maps $m$ to the interval $[0,1]$, with $m=r_{\text{min}}$ mapped to $0$ and $m=r_{\text{max}}$ mapped to $1$.

 3. Multiplying this by $(t_{\text{max}}-t_{\text{min}})$ maps $m$ to $[0,t_{\text{max}}-t_{\text{min}}]$.

 4. Finally, adding $t_{\text{min}}$ shifts everything and maps $m$ to $[t_{\text{min}},t_{\text{max}}]$ as desired.