Help with timings

so, i'm building 8-step sequencer using arduino ide, , got part configure period duration using pot. , work, doesn't work way expect. i've been looking @ code hours, , can't figure out went wrong, hoping here give me hand 

here's relevant code, "loop" section:

code: [select]

  // playing speed regulation, using pot:
  int speedpot = analogread(pot1); // pot determines t duration
  float t_step = 0.89; // [ms], t_step=(1000ms-100ms)/1024
  float t = 100 + speedpot * t_step; // [ms], t= t_on + t_off, length of 1 period


  if (millis() - t_timer < t) { // step scope
   digitalwrite(led[stepcounter], high);
  } else { // time t passed, time move on
    t_timer = millis();
    digitalwrite(led[stepcounter], low);
    if (stepcounter == 7)
      stepcounter = 0;
    else
      stepcounter++;
  }

so, first part determining t duration. wanted go 0.1-1 s, or, 100+[0-1023]*0.89 [ms], roughly.

my sequencer has 8 leds, , in second part wanted test setup turning each led period t, , jumping next period/led, t determined pot position. , that, instead of 0.1-1s, around 2-20s. did wrong?

i declared timers type "long", t used type "float". problem, can 2 in equation?

i attach whole code if needed, it's still under construction, it's messy.

quote

i declared timers type "long",

they should unsigned long match value returned millis() , avoid possible problems negative values.

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