diff --git a/lib/vfd.c b/lib/vfd.c
index e6ddf95..46a0e50 100644
--- a/lib/vfd.c
+++ b/lib/vfd.c
@@ -302,13 +302,13 @@ static const uint8_t pict5x7[][5] = {
 
 /* the 32 bits values to be shifted out to the VFD driver
  * split into 16 bit for SPI transfer
- * since the bits for digits and matrix are independant, they can be conbined
+ * since the bits for digits and matrix are independent, they can be combined
  * we have more matrix (12) than digits (10)
  */
 static uint16_t driver_data[VFD_MATRIX][VFD_DRIVERS*2] = {0};
 static volatile uint8_t spi_i = 0; // which driver data is being transmitted
-static volatile uint8_t vfd_mux = 0; // which part to output
-static const uint32_t digit_mask = 0x00fff0; // the bits used for selecting then digit and 7 segment anodes (for the second driver)
+static volatile uint8_t vfd_grid = 0; // which grid/part to activate (single digits and matrix can be combined)
+static const uint32_t digit_mask = 0x00fffff0; // the bits used for selecting then digit and 7 segment anodes (for the second driver)
 
 /* set digit <nb> to ASCII character <c>
  * use the MSB of <c> to enable the dot */
@@ -478,7 +478,7 @@ void vfd_setup(void)
 	timer_reset(VFD_TIMER); // reset timer state
 	timer_set_mode(VFD_TIMER, TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE, TIM_CR1_DIR_UP); // set timer mode, use undivided timer clock,edge alignment (simple count), and count up
 	timer_set_prescaler(VFD_TIMER, (SYSTEM_CLOCK_FREQ/(1<<16))-1); // set the prescaler so this 16 bits timer overflows at 1Hz
-	timer_set_period(VFD_TIMER, 0xffff/(VFD_DIGITS+VFD_MATRIX)/150); // set the refresh frequency
+	timer_set_period(VFD_TIMER, 0xffff/LENGTH(driver_data)/100); // set the refresh frequency
 	timer_enable_irq(VFD_TIMER, TIM_DIER_UIE); // enable interrupt for timer
 	nvic_enable_irq(VFD_TIMER_IRQ); // allow interrupt for timer
 	
@@ -494,7 +494,7 @@ void spi2_isr(void)
 	if (SPI_SR(VFD_SPI) & SPI_SR_TXE) { // transmission buffer empty
 		if (spi_i<LENGTH(driver_data[0])) { // check if data is available
 			gpio_clear(VFD_PORT, VFD_NLE); // slave select to latch data
-			spi_send(VFD_SPI, driver_data[vfd_mux][spi_i++]); // send next data
+			spi_send(VFD_SPI, driver_data[vfd_grid][spi_i++]); // send next data
 		} else { // all data transmitted
 			spi_disable_tx_buffer_empty_interrupt(VFD_SPI); // no need to wait for new data
 			while (SPI_SR(VFD_SPI) & SPI_SR_BSY); // wait for data to be shifted out
@@ -520,6 +520,6 @@ void tim5_isr(void)
 		timer_clear_flag(VFD_TIMER, TIM_SR_UIF); // clear flag
     	spi_i = 0; // set the register to shift out
 		spi_enable_tx_buffer_empty_interrupt(VFD_SPI); // enable TX empty interrupt
-		vfd_mux = (vfd_mux+1)%LENGTH(driver_data); // got to next segment
+		vfd_grid = (vfd_grid+1)%LENGTH(driver_data); // got to next segment
 	}
 }