Oops! Let me change that sequence slightly...

P = 1000 * (U- 1)*U/ 2
or...
P = 500*(U-1)*U

Therefore, try this equation instead given points 'P'

=INT((25 + SQRT(5)*SQRT(125 + P))/50)

--
HTH. :)
Dana DeLouis
Windows XP, Office 2003

<snip

Points_______Units
0___________1
1000________2 [0+1*Delta = 1000]
3000________3 [1000+2*Delta = 3000]
6000________4 [3000+3*Delta = 6000]
10000_______5 [6000+4*Delta = 10000]
15000_______6 [10000+5*Delta = 15000]
21000_______7 [15000+6*Delta = 21000]
28000_______8 [21000+7*Delta = 28000]